What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Helicase Use of ATP: Mechanism, Energy Coupling, and Biological Roles

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Introduction to Helicases and ATP

What Are Helicases?

Helicases are a class of molecular motor enzymes that catalyze the separation of double-stranded nucleic acids into single strands. They are found in all domains of life and participate in virtually every process involving nucleic acid metabolism, including DNA replication, repair, recombination, transcription, and RNA processing. The fundamental reaction they perform—strand separation—requires energy input because the hydrogen bonds between complementary bases and the base-stacking interactions within the duplex must be overcome. The energy for this work comes from the hydrolysis of adenosine triphosphate (ATP). The term "helicase use ATP" describes this central dependency: without ATP binding and hydrolysis, helicases cannot translocate along nucleic acids or unwind duplexes.

The Helicase Definition encompasses a broad family of enzymes, but all share a common architectural core that binds ATP and nucleic acid. The Helicase Enzyme is not a passive binder of DNA; it is an active motor that converts chemical energy into mechanical motion. This energy conversion is what distinguishes helicases from single-stranded DNA binding proteins, which stabilize unwound DNA but do not actively separate it.

Why ATP Is the Fuel for Unwinding

ATP is the universal energy currency of the cell, and helicases exploit its free energy of hydrolysis. The phosphoanhydride bonds between the β- and γ-phosphates of ATP store approximately 30.5 kJ/mol of free energy under standard conditions. When ATP is hydrolyzed to ADP and inorganic phosphate (Pi), this energy is released and can be harnessed to perform mechanical work.

Why ATP rather than another nucleotide? Several properties make ATP particularly suited for this role. First, the cell maintains ATP concentrations at millimolar levels (typically 1–10 mM), providing a large thermodynamic driving force. Second, the hydrolysis reaction is kinetically stable in the absence of enzymes, meaning ATP will not spontaneously decompose, allowing the helicase to control precisely when hydrolysis occurs. Third, the products of hydrolysis—ADP and Pi—are easily released and recycled, enabling rapid catalytic turnover. Some helicases can use other nucleoside triphosphates (e.g., GTP, CTP, UTP) with reduced efficiency, but ATP is the preferred substrate for the vast majority.

The ATP Hydrolysis Cycle in Helicases

The ATP hydrolysis cycle in helicases follows a sequence of discrete steps, each coupled to a conformational change in the enzyme. This cycle is the engine that drives mechanical motion.

ATP Binding and Conformational Change

The cycle begins with the helicase in an "open" or "apo" conformation, with low affinity for nucleic acid. ATP binds to the nucleotide-binding pocket formed by conserved motifs within the helicase core. ATP binding induces a conformational change that closes the cleft between two RecA-like domains (described in Section 4). This closure is transmitted to the DNA-binding surfaces of the enzyme, increasing their affinity for single-stranded DNA (ssDNA).

The binding step is rapid and reversible. The equilibrium constant for ATP binding is typically in the micromolar range, meaning that at cellular ATP concentrations (millimolar), the enzyme is saturated with ATP. The conformational change upon ATP binding is often described as a transition from a "relaxed" to a "tense" state, where the enzyme grips the nucleic acid more tightly. This is the first step in converting chemical binding energy into mechanical strain.

Hydrolysis and Phosphate Release

Once ATP is bound and the enzyme has adopted its closed conformation, hydrolysis occurs. The catalytic machinery positions a water molecule for nucleophilic attack on the γ-phosphate of ATP. This reaction is facilitated by a conserved aspartate or glutamate residue that activates the water molecule and a conserved lysine that stabilizes the transition state.

Hydrolysis itself produces ADP and Pi, but the energy release is not instantaneous. The products remain bound to the enzyme, and the system is in a high-energy state. The subsequent release of inorganic phosphate is the key step that triggers a major conformational change. Phosphate release is often the rate-limiting step of the cycle and is coupled to the "power stroke" that drives the enzyme forward along the nucleic acid. After Pi release, the enzyme adopts a conformation with altered DNA affinity, typically releasing the DNA at the trailing edge while maintaining grip at the leading edge.

ADP Release and Reset

The final step is the release of ADP, which returns the enzyme to its open, low-affinity conformation. ADP release is also coupled to conformational changes that reset the enzyme for another round of ATP binding. The complete cycle—ATP binding, hydrolysis, Pi release, ADP release—takes between 0.1 and 10 milliseconds depending on the helicase and conditions. This corresponds to turnover numbers of 1–50 ATP molecules hydrolyzed per second per enzyme molecule.

The cycle is not perfectly efficient. Some helicases exhibit "futile" hydrolysis, where ATP is hydrolyzed without productive translocation. This occurs when the enzyme hydrolyzes ATP but fails to couple the energy to movement, often because the nucleic acid substrate is not properly positioned. The ratio of productive to futile cycles varies among helicases and is a target of regulation.

Coupling ATP Hydrolysis to Mechanical Work

The central question in helicase mechanochemistry is how the chemical energy of ATP hydrolysis is converted into the mechanical work of breaking hydrogen bonds and moving along DNA. Two principal models have been proposed: the power stroke model and the Brownian ratchet model. In practice, most helicases use a combination of both.

The Power Stroke Model

The power stroke model posits that ATP hydrolysis and product release drive a large, directed conformational change in the enzyme, much like the release of a compressed spring. In this model, the enzyme binds ATP in one conformation, hydrolyzes it, and then undergoes a dramatic structural rearrangement that physically pushes the enzyme forward along the nucleic acid.

For helicases, the power stroke is typically associated with the closure and opening of the ATP-binding cleft. ATP binding closes the cleft, pulling two domains together. This closure is coupled to a change in the position of DNA-binding loops, effectively "pulling" the DNA through the enzyme. Phosphate release then triggers cleft opening, which releases the DNA at one end while the other end maintains grip. The net effect is a stepwise movement along the nucleic acid.

The power stroke model predicts that the step size (the distance moved per ATP hydrolyzed) is determined by the magnitude of the conformational change. For many helicases, this step size is 1–2 nucleotides per ATP, though some hexameric helicases move in larger steps of 2–3 nucleotides.

Brownian Ratchet and Inchworm Mechanisms

The Brownian ratchet model takes a different view. In this model, thermal fluctuations constantly move the enzyme forward and backward along the nucleic acid. The enzyme does not "push" itself forward; instead, it biases the random thermal motion by binding ATP and hydrolyzing it in a way that prevents backward movement.

In the Brownian ratchet model, the enzyme oscillates between states with different DNA affinities. When ATP is bound, the enzyme has high affinity for DNA and "locks" onto the strand. When ATP is hydrolyzed and products are released, the enzyme adopts a low-affinity state and can diffuse. The free energy of ATP hydrolysis is used to create an energy landscape that favors forward movement over backward movement, effectively acting as a ratchet.

The inchworm mechanism is a specific implementation of these principles for monomeric or dimeric helicases. In this model, the helicase has two DNA-binding sites that alternate between high and low affinity states. ATP binding and hydrolysis cause these sites to alternately grip and release the DNA, allowing the enzyme to "inch" along the strand. One site maintains contact with the DNA at all times, preventing dissociation. This mechanism is used by many superfamily 1 and 2 helicases, such as the bacterial helicase UvrD and the eukaryotic helicase PcrA.

The distinction between power stroke and Brownian ratchet is not absolute. Most helicases exhibit elements of both. The power stroke provides the directional bias, while thermal fluctuations provide the mobility. The relative contribution of each varies among helicases and is an active area of research.

Structural Features of the ATPase Core

RecA Fold and Helicase Superfamilies

All helicases share a core structural domain that resembles the bacterial recombination protein RecA. This RecA fold consists of a central β-sheet flanked by α-helices, forming a nucleotide-binding pocket. The RecA fold is the engine of the helicase: it binds ATP, hydrolyzes it, and undergoes the conformational changes that drive movement.

Helicases are classified into six superfamilies (SF1–SF6) based on the number and arrangement of RecA domains and the presence of additional structural features. SF1 and SF2 are the largest and most diverse, containing monomeric or dimeric helicases that translocate along single-stranded DNA or RNA. SF3–SF6 are predominantly hexameric helicases that form ring-shaped structures and encircle nucleic acid.

The Helicase Structure of SF1 and SF2 helicases consists of two RecA-like domains (often called domains 1A and 2A, or domains 1 and 2) connected by a flexible linker. The ATP-binding site is formed at the interface between these two domains, with residues from both domains contributing to nucleotide binding and hydrolysis. This arrangement means that ATP binding and hydrolysis directly modulate the relative orientation of the two domains, which in turn controls DNA binding and movement.

Key Motifs and Their Functions

The ATPase core of helicases contains a set of conserved sequence motifs that mediate nucleotide binding, hydrolysis, and coupling to DNA movement. These motifs are the molecular machinery of the helicase.

Walker A motif (P-loop): This motif, with the consensus sequence GxxxxGKT/S, forms a phosphate-binding loop that interacts with the β- and γ-phosphates of ATP. The conserved lysine is essential for ATP binding; mutation of this residue typically abolishes ATPase activity. The Walker A motif is also called the P-loop (phosphate-binding loop).

Walker B motif: This motif, with the consensus sequence hhhhDExx (where h is a hydrophobic residue), contains an aspartate that coordinates the catalytic water molecule and a glutamate that activates it for nucleophilic attack. The Walker B motif is essential for hydrolysis but not for ATP binding.

Motif III (Sensor I): This motif contains a conserved asparagine or histidine that senses the presence of the γ-phosphate and couples ATP binding to conformational changes in the DNA-binding domains.

Motif IV (Sensor II): This motif contains an arginine that interacts with the γ-phosphate and helps position the nucleotide for hydrolysis. It is sometimes called the "arginine finger" and is critical for coupling hydrolysis to mechanical work.

Motif Ia, II, and others: Additional motifs (Ia, II, III, IV, V, VI in SF1; Q, I, Ia, Ib, II, III, IV, V, VI in SF2) contribute to DNA binding and to the coupling of ATP hydrolysis to translocation. Motif II contains the DEAD or DEAH box in SF2 helicases, giving rise to the DEAD-box helicase family.

The coordination between ATP binding and DNA binding is bidirectional. ATP binding increases DNA affinity, and DNA binding stimulates ATP hydrolysis. This mutual stimulation ensures that the helicase does not waste ATP when it is not bound to nucleic acid. The basal ATPase rate of most helicases in the absence of DNA is very low (less than 1% of the stimulated rate), but increases dramatically (10- to 100-fold) when the helicase binds to ssDNA.

Experimental Evidence for ATP-Driven Unwinding

Biochemical Assays

The requirement for ATP in helicase activity was established through classic biochemical experiments. In a standard helicase assay, a radiolabeled oligonucleotide is annealed to a complementary strand to form a partial duplex. The helicase is added along with ATP, and the reaction is allowed to proceed at 37°C for 10–30 minutes. The products are then separated by native polyacrylamide gel electrophoresis, which resolves single-stranded from double-stranded DNA. Unwinding is detected as the appearance of the radiolabeled single-stranded product.

Control experiments demonstrate the ATP dependence. When ATP is omitted or replaced with a non-hydrolyzable analog such as AMP-PNP (adenylyl-imidodiphosphate), no unwinding is observed. AMP-PNP binds to the helicase and induces the closed conformation but cannot be hydrolyzed, trapping the enzyme in a high-affinity DNA-binding state. This experiment demonstrates that ATP binding alone is insufficient for unwinding; hydrolysis is required.

ATPase assays measure the rate of ATP hydrolysis directly. In these assays, helicase is incubated with [γ-32P]ATP or with a coupled enzyme system that links ADP production to NADH oxidation, which can be monitored spectrophotometrically at 340 nm. Typical reaction conditions include 20–50 mM Tris-HCl (pH 7.5), 50–100 mM NaCl or KCl, 5–10 mM MgCl2, 1–2 mM ATP, and 1–10 nM helicase. The Mg2+ is essential because the true substrate is Mg-ATP2−, not free ATP. The ATPase rate is measured in molecules of ATP hydrolyzed per helicase per second (s−1). For the E. coli helicase DnaB, this rate is approximately 20–30 s−1 in the presence of ssDNA.

Single-Molecule Studies

Single-molecule techniques have provided direct evidence for ATP-driven movement and have revealed mechanistic details that are obscured in bulk assays.

Optical tweezers use a focused laser beam to trap a microscopic bead attached to a DNA molecule. By measuring the displacement of the bead, researchers can track the position of a helicase as it unwinds DNA in real time. These experiments have shown that helicases move in discrete steps and that the step size is coupled to ATP hydrolysis. For example, single-molecule studies of the bacteriophage T7 helicase gp4 have revealed steps of 2–3 base pairs per ATP hydrolyzed.

Single-molecule Förster resonance energy transfer (smFRET) uses the distance-dependent energy transfer between two fluorescent dyes to monitor conformational changes in the helicase or the separation of DNA strands. In a typical experiment, a donor fluorophore is attached to one strand of a DNA duplex and an acceptor fluorophore to the complementary strand. As the helicase unwinds the duplex, the strands separate, and the FRET efficiency decreases. This approach has been used to demonstrate that helicases unwind DNA in a stepwise manner and that the rate of unwinding is proportional to ATP concentration.

Magnetic tweezers apply force to a magnetic bead attached to DNA and can measure both unwinding and supercoiling. These experiments have shown that helicases can generate forces of several piconewtons (pN) during unwinding, sufficient to overcome the stability of the DNA duplex.

Helicase Processivity and Directionality

Processivity and Step Size

Processivity is a measure of how many base pairs a helicase can unwind before dissociating from the DNA. It is defined as the probability that the enzyme will continue to the next step rather than fall off. Processivity is typically expressed as the number of base pairs unwound per binding event or as the processivity factor, which is the probability of continuing per step.

The processivity of helicases varies widely. Some helicases, such as the replicative helicase DnaB, are highly processive and can unwind tens of thousands of base pairs without dissociating. Others, such as many repair helicases, are poorly processive and unwind only 10–100 base pairs per binding event. Low processivity is not a defect; it is often advantageous for repair helicases, which need to unwind short regions of DNA and then dissociate.

The step size is the number of base pairs unwound per ATP hydrolyzed. This value is not fixed and can vary depending on the helicase and the conditions. For SF1 and SF2 helicases, the step size is typically 1–2 base pairs per ATP. For hexameric helicases, the step size is often larger, ranging from 2–3 base pairs per ATP for the T7 gp4 helicase to 3–4 base pairs per ATP for the E. coli Rho transcription terminator.

Polarity of Translocation

Helicases have a defined directionality of translocation along single-stranded DNA. This directionality is determined by the orientation of the helicase on the DNA and is an intrinsic property of the enzyme.

3' to 5' helicases translocate along ssDNA in the 3' to 5' direction. They are typically loaded onto the lagging strand at a replication fork or onto the single-stranded region of a DNA repair intermediate. Examples include E. coli UvrD, the yeast helicase Srs2, and the human helicase BLM (Bloom syndrome protein).

5' to 3' helicases translocate in the opposite direction. They are loaded onto the leading strand or onto the opposite side of a repair intermediate. Examples include E. coli RecBCD (which has both 3' to 5' and 5' to 3' activities in different subunits), the yeast helicase Rrm3, and the human helicase WRN (Werner syndrome protein).

The directionality is determined by the geometry of the DNA-binding site. The helicase binds ssDNA with a specific polarity, and the ATP-driven conformational changes move the enzyme in a direction dictated by this polarity. The Replication Fork Helicase DnaB is a 5' to 3' helicase that encircles the lagging strand and translocates in the same direction as the replication fork, unwinding the duplex ahead of the polymerase.

Regulation of ATPase Activity

Accessory Factors

Helicases rarely work alone. Accessory proteins modulate their ATPase activity, processivity, and substrate specificity. These factors can be classified as stimulators, inhibitors, or loaders.

Stimulators increase the ATPase rate or processivity of a helicase. The E. coli helicase DnaB is stimulated by the helicase loader DnaC, which facilitates loading of DnaB onto the origin of replication. The single-stranded DNA binding protein (SSB) also stimulates DnaB by removing secondary structure from the ssDNA and by directly interacting with the helicase. In eukaryotes, the CMG complex (Cdc45-MCM-GINS) is a multi-subunit helicase in which the GINS proteins stimulate the ATPase activity of the MCM (minichromosome maintenance) motor.

Inhibitors reduce helicase ATPase activity. The E. coli protein Tus (terminus utilization substance) binds to specific DNA sequences called Ter sites and arrests the replication fork by inhibiting DnaB. The mechanism involves both direct protein-protein interaction and the formation of a protein-DNA complex that blocks DnaB translocation.

Loaders are specialized proteins that place the helicase onto its substrate. The eukaryotic origin recognition complex (ORC) and Cdc6 load the MCM helicase onto DNA during replication initiation. The loader uses ATP binding and hydrolysis to remodel the helicase and DNA, enabling the helicase to encircle the DNA.

Regulatory Modifications

Post-translational modifications regulate helicase ATPase activity in response to cellular signals.

Phosphorylation is the most common modification. The human helicase BLM is phosphorylated by the ATM (ataxia-telangiectasia mutated) kinase in response to DNA damage. This phosphorylation reduces the ATPase activity of BLM and alters its interaction with other repair proteins. The yeast helicase Srs2 is phosphorylated by cyclin-dependent kinase (CDK) during the cell cycle, which regulates its role in homologous recombination.

Ubiquitination targets helicases for degradation or alters their activity. The human helicase FANCM (Fanconi anemia complementation group M) is ubiquitinated in response to replication stress, which promotes its recruitment to stalled replication forks.

Acetylation and SUMOylation also regulate helicase activity. The tumor suppressor p53 acetylates the helicase WRN, increasing its ATPase activity. SUMOylation of the yeast helicase Sgs1 regulates its localization and activity during meiosis.

The regulation of helicase ATPase activity is critical for genome stability. Unregulated helicase activity can lead to excessive unwinding, DNA damage, and genomic instability. Conversely, insufficient helicase activity leads to replication stress and cell death.

Common Pitfalls and Misconceptions

Misconception: ATP Directly Breaks Base Pairs

A common error is to think that the energy from ATP hydrolysis is used to directly break the hydrogen bonds between base pairs. This is incorrect. The hydrogen bonds between complementary bases are relatively weak (2–3 hydrogen bonds per base pair, corresponding to approximately 10–20 kJ/mol). The free energy of ATP hydrolysis (approximately 30–50 kJ/mol under cellular conditions) is more than sufficient to break these bonds.

However, the helicase does not use ATP energy to "melt" the DNA. Instead, the helicase uses ATP to translocate along the DNA, and the mechanical force of translocation is what separates the strands. The helicase acts as a wedge that physically separates the two strands as it moves. The energy from ATP hydrolysis is used to move the helicase, and the movement of the helicase is what breaks the hydrogen bonds.

This distinction is important for understanding the mechanism. The Helicase Break Hydrogen Bonds process is an indirect consequence of translocation, not a direct consequence of ATP hydrolysis. The helicase does not "burn" ATP to melt the DNA; it burns ATP to move, and the movement melts the DNA.

Misconception: All Helicases Work the Same Way

Another common error is to assume that all helicases use identical mechanisms. While all helicases use ATP and share the RecA fold, the details of their mechanisms differ substantially.

Monomeric helicases such as PcrA and UvrD translocate as monomers or dimers and use an inchworm mechanism. They have relatively low processivity and are involved in repair and recombination.

Hexameric helicases such as DnaB, MCM, and Rho form ring-shaped structures that encircle DNA. They use a different mechanism, often described as a "pump" or "screw" mechanism, where the ring rotates or undergoes sequential conformational changes to push DNA through the central channel. These helicases are typically highly processive and are involved in replication and transcription termination.

DEAD-box helicases such as eIF4A and Ded1 are a subclass of SF2 helicases that do not translocate processively along DNA or RNA. Instead, they unwind short duplexes by locally destabilizing the duplex and then dissociating. They use ATP to drive a conformational change that "pops" open the duplex, but they do not move along the nucleic acid.

The RNA Helicase family is particularly diverse. Some RNA helicases unwind RNA duplexes, while others remodel RNA-protein complexes (RNPs) without unwinding RNA. The DEAD-box helicase eIF4A unwinds secondary structure in the 5' untranslated region of mRNAs to facilitate ribosome binding, while the helicase RIG-I (retinoic acid-inducible gene I) uses ATP to translocate along double-stranded RNA and signal the presence of viral RNA.

Misconception: Helicases Are the Same as Topoisomerases

Students sometimes confuse helicases with topoisomerases. This is incorrect. Helicase a Topoisomerase is a false equivalence. Topoisomerases change the linking number of DNA by breaking and rejoining the phosphodiester backbone, thereby relieving supercoiling. Helicases do not break the DNA backbone; they separate the strands of a duplex. The two enzymes work together during replication: helicases unwind the duplex, and topoisomerases relieve the positive supercoiling that accumulates ahead of the replication fork.

Misconception: ATP Binding Alone Is Sufficient

Some students believe that ATP binding, not hydrolysis, is sufficient for helicase activity. This is incorrect. Non-hydrolyzable ATP analogs such as AMP-PNP bind to helicases and induce the closed conformation, but they do not support unwinding. The enzyme becomes trapped in a high-affinity DNA-binding state and cannot complete the cycle. This demonstrates that ATP binding is necessary but not sufficient; hydrolysis and product release are required for the enzyme to complete its catalytic cycle and move along the DNA.

Frequently Asked Questions

Does helicase use ATP?

Yes. Helicases are ATP-dependent enzymes. They bind ATP, hydrolyze it to ADP and inorganic phosphate, and use the free energy of hydrolysis to drive conformational changes that result in nucleic acid unwinding and translocation. Without ATP, helicases cannot unwind DNA or RNA duplexes. The requirement for ATP is absolute and can be demonstrated by the complete loss of helicase activity when ATP is omitted from the reaction or replaced with a non-hydrolyzable analog.

How does helicase use ATP?

Helicases use ATP through a multi-step catalytic cycle. First, ATP binds to the nucleotide-binding pocket formed by the Walker A and Walker B motifs. ATP binding induces a conformational change that closes the cleft between the two RecA domains and increases the helicase's affinity for nucleic acid. Second, the ATP is hydrolyzed to ADP and inorganic phosphate. Third, phosphate is released, triggering a major conformational change that drives the helicase forward along the nucleic acid. Finally, ADP is released, returning the enzyme to its open, low-affinity conformation. This cycle repeats, allowing the helicase to move processively along the DNA or RNA.

Why does helicase need ATP?

Helicases need ATP because the unwinding of double-stranded nucleic acids is thermodynamically unfavorable. The hydrogen bonds between complementary bases and the base-stacking interactions within the duplex must be overcome. ATP hydrolysis provides the free energy required to drive this process. Additionally, ATP hydrolysis allows the helicase to move directionally along the nucleic acid, which is essential for processive unwinding. The energy from ATP is used to power the mechanical movement of the helicase, and this movement physically separates the two strands.

What happens if helicase cannot hydrolyze ATP?

If a helicase cannot hydrolyze ATP, it cannot unwind DNA or RNA. This can occur through mutation of critical catalytic residues (such as the Walker A lysine or the Walker B aspartate/glutamate) or through treatment with non-hydrolyzable ATP analogs. In either case, the helicase binds ATP (or the analog) and adopts the closed, high-affinity DNA-binding conformation, but it cannot progress through the hydrolysis and product release steps. The helicase becomes trapped on the nucleic acid, unable to move or dissociate. In cells, this can lead to replication fork stalling, DNA damage, and cell death.

Is ATP hydrolysis directly breaking hydrogen bonds?

No. ATP hydrolysis does not directly break hydrogen bonds between base pairs. The energy from ATP hydrolysis is used to power the mechanical translocation of the helicase along the nucleic acid. As the helicase moves, it acts as a wedge that physically separates the two strands. The hydrogen bonds are broken by the mechanical force of the moving helicase, not by the chemical energy of ATP hydrolysis directly. This is an important distinction: the helicase uses ATP to move, and the movement separates the strands.

How many ATP molecules does helicase use per base pair unwound?

The number of ATP molecules hydrolyzed per base pair unwound varies among helicases. For SF1 and SF2 helicases, the step size is typically 1–2 base pairs per ATP hydrolyzed. For hexameric helicases, the step size is often larger, ranging from 2–3 base pairs per ATP for the T7 gp4 helicase. However, these values are not fixed and can vary depending on the helicase, the substrate, and the experimental conditions. The measured values also depend on the efficiency of coupling between ATP hydrolysis and translocation; some ATP is always hydrolyzed without productive movement.

Do all helicases use ATP?

The vast majority of helicases use ATP as their energy source. However, a small number of helicases can use other nucleoside triphosphates. For example, the E. coli helicase DnaB can hydrolyze all four ribonucleoside triphosphates (ATP, GTP, CTP, UTP), though ATP is the preferred substrate. Some RNA helicases can use GTP with reduced efficiency. However, no helicase has been identified that operates without a nucleoside triphosphate energy source. The use of ATP is a defining feature of the helicase family.

Key Takeaways

Helicases are ATP-dependent molecular motors that unwind double-stranded nucleic acids by translocating along single-stranded DNA or RNA.
The ATP hydrolysis cycle consists of four steps: ATP binding, hydrolysis, phosphate release, and ADP release, each coupled to specific conformational changes in the enzyme.
ATP hydrolysis does not directly break hydrogen bonds; instead, the energy is used to power mechanical movement that physically separates the strands.
All helicases share a conserved RecA fold core containing Walker A and Walker B motifs, but they are classified into six superfamilies with distinct mechanisms and functions.
Helicases exhibit defined directionality (3' to 5' or 5' to 3') and variable processivity, determined by their structure and biological role.
The Helicase Protein family includes both monomeric and hexameric enzymes, with hexameric helicases forming rings that encircle DNA.
Helicase ATPase activity is regulated by accessory proteins, post-translational modifications, and DNA structure, ensuring proper coordination with replication, repair, and transcription processes.