1
|
Structural insight and characterization of human Twinkle helicase in mitochondrial disease. Proc Natl Acad Sci U S A 2022; 119:e2207459119. [PMID: 35914129 PMCID: PMC9371709 DOI: 10.1073/pnas.2207459119] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Twinkle is the mammalian helicase vital for replication and integrity of mitochondrial DNA. Over 90 Twinkle helicase disease variants have been linked to progressive external ophthalmoplegia and ataxia neuropathies among other mitochondrial diseases. Despite the biological and clinical importance, Twinkle represents the only remaining component of the human minimal mitochondrial replisome that has yet to be structurally characterized. Here, we present 3-dimensional structures of human Twinkle W315L. Employing cryo-electron microscopy (cryo-EM), we characterize the oligomeric assemblies of human full-length Twinkle W315L, define its multimeric interface, and map clinical variants associated with Twinkle in inherited mitochondrial disease. Cryo-EM, crosslinking-mass spectrometry, and molecular dynamics simulations provide insight into the dynamic movement and molecular consequences of the W315L clinical variant. Collectively, this ensemble of structures outlines a framework for studying Twinkle function in mitochondrial DNA replication and associated disease states.
Collapse
|
2
|
Bocanegra R, Ismael Plaza GA, Pulido CR, Ibarra B. DNA replication machinery: Insights from in vitro single-molecule approaches. Comput Struct Biotechnol J 2021; 19:2057-2069. [PMID: 33995902 PMCID: PMC8085672 DOI: 10.1016/j.csbj.2021.04.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 04/03/2021] [Accepted: 04/03/2021] [Indexed: 11/16/2022] Open
Abstract
The replisome is the multiprotein molecular machinery that replicates DNA. The replisome components work in precise coordination to unwind the double helix of the DNA and replicate the two strands simultaneously. The study of DNA replication using in vitro single-molecule approaches provides a novel quantitative understanding of the dynamics and mechanical principles that govern the operation of the replisome and its components. ‘Classical’ ensemble-averaging methods cannot obtain this information. Here we describe the main findings obtained with in vitro single-molecule methods on the performance of individual replisome components and reconstituted prokaryotic and eukaryotic replisomes. The emerging picture from these studies is that of stochastic, versatile and highly dynamic replisome machinery in which transient protein-protein and protein-DNA associations are responsible for robust DNA replication.
Collapse
Affiliation(s)
- Rebeca Bocanegra
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - G A Ismael Plaza
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - Carlos R Pulido
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - Borja Ibarra
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| |
Collapse
|
3
|
Harman A, Barth C. The Dictyostelium discoideum homologue of Twinkle, Twm1, is a mitochondrial DNA helicase, an active primase and promotes mitochondrial DNA replication. BMC Mol Biol 2018; 19:12. [PMID: 30563453 PMCID: PMC6299598 DOI: 10.1186/s12867-018-0114-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Accepted: 11/07/2018] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND DNA replication requires contributions from various proteins, such as DNA helicases; in mitochondria Twinkle is important for maintaining and replicating mitochondrial DNA. Twinkle helicases are predicted to also possess primase activity, as has been shown in plants; however this activity appears to have been lost in metazoans. Given this, the study of Twinkle in other organisms is required to better understand the evolution of this family and the roles it performs within mitochondria. RESULTS Here we describe the characterization of a Twinkle homologue, Twm1, in the amoeba Dictyostelium discoideum, a model organism for mitochondrial genetics and disease. We show that Twm1 is important for mitochondrial function as it maintains mitochondrial DNA copy number in vivo. Twm1 is a helicase which unwinds DNA resembling open forks, although it can act upon substrates with a single 3' overhang, albeit less efficiently. Furthermore, unlike human Twinkle, Twm1 has primase activity in vitro. Finally, using a novel in bacterio approach, we demonstrated that Twm1 promotes DNA replication. CONCLUSIONS We conclude that Twm1 is a replicative mitochondrial DNA helicase which is capable of priming DNA for replication. Our results also suggest that non-metazoan Twinkle could function in the initiation of mitochondrial DNA replication. While further work is required, this study has illuminated several alternative processes of mitochondrial DNA maintenance which might also be performed by the Twinkle family of helicases.
Collapse
Affiliation(s)
- Ashley Harman
- Department of Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, VIC Australia
- Present Address: Cell Biology Unit, Children’s Medical Research Institute, University of Sydney, Westmead, NSW Australia
| | - Christian Barth
- Department of Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, VIC Australia
| |
Collapse
|
4
|
Gupta A, Patil S, Vijayakumar R, Kondabagil K. The Polyphyletic Origins of Primase-Helicase Bifunctional Proteins. J Mol Evol 2017; 85:188-204. [PMID: 29143083 DOI: 10.1007/s00239-017-9816-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Accepted: 10/28/2017] [Indexed: 11/28/2022]
Abstract
We studied the evolutionary relationships of different primase-helicase bifunctional proteins, found mostly in viruses, virophages, plasmids, and organellar genomes, by phylogeny and correlation analysis. Our study suggests independent origins of primase-helicase bifunctional proteins resulting from multiple fusion events between genes encoding primase and helicase domains of different families. The correlation analysis further indicated strong functional dependencies of domains in the bifunctional proteins that are part of smaller genomes and plasmids. Bifunctional proteins found in some bacterial genomes exhibited weak coevolution probably suggesting that these are the non-functional remnants of the proteins acquired via horizontal transfer. We have put forward possible scenarios for the origin of primase-helicase bifunctional proteins in large eukaryotic DNA viruses and virophages.
Collapse
Affiliation(s)
- Ankita Gupta
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
| | - Supriya Patil
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
| | - Ramya Vijayakumar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
| | - Kiran Kondabagil
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
| |
Collapse
|
5
|
Brennan LD, Forties RA, Patel SS, Wang MD. DNA looping mediates nucleosome transfer. Nat Commun 2016; 7:13337. [PMID: 27808093 PMCID: PMC5097161 DOI: 10.1038/ncomms13337] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Accepted: 09/23/2016] [Indexed: 01/18/2023] Open
Abstract
Proper cell function requires preservation of the spatial organization of chromatin modifications. Maintenance of this epigenetic landscape necessitates the transfer of parental nucleosomes to newly replicated DNA, a process that is stringently regulated and intrinsically linked to replication fork dynamics. This creates a formidable setting from which to isolate the central mechanism of transfer. Here we utilized a minimal experimental system to track the fate of a single nucleosome following its displacement, and examined whether DNA mechanics itself, in the absence of any chaperones or assembly factors, may serve as a platform for the transfer process. We found that the nucleosome is passively transferred to available dsDNA as predicted by a simple physical model of DNA loop formation. These results demonstrate a fundamental role for DNA mechanics in mediating nucleosome transfer and preserving epigenetic integrity during replication.
Collapse
Affiliation(s)
- Lucy D Brennan
- Department of Physics-Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Robert A Forties
- Department of Physics-Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA.,Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, USA
| | - Smita S Patel
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
| | - Michelle D Wang
- Department of Physics-Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA.,Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, USA
| |
Collapse
|
6
|
Sun B, Wang MD. Single-Molecule Optical-Trapping Techniques to Study Molecular Mechanisms of a Replisome. Methods Enzymol 2016; 582:55-84. [PMID: 28062045 DOI: 10.1016/bs.mie.2016.08.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The replisome is a multiprotein molecular machinery responsible for the replication of DNA. It is composed of several specialized proteins each with dedicated enzymatic activities, and in particular, helicase unwinds double-stranded DNA and DNA polymerase catalyzes the synthesis of DNA. Understanding how a replisome functions in the process of DNA replication requires methods to dissect the mechanisms of individual proteins and of multiproteins acting in concert. Single-molecule optical-trapping techniques have proved to be a powerful approach, offering the unique ability to observe and manipulate biomolecules at the single-molecule level and providing insights into the mechanisms of molecular motors and their interactions and coordination in a complex. Here, we describe a practical guide to applying these techniques to study the dynamics of individual proteins in the bacteriophage T7 replisome, as well as the coordination among them. We also summarize major findings from these studies, including nucleotide-specific helicase slippage and new lesion bypass pathway in T7 replication.
Collapse
Affiliation(s)
- B Sun
- School of Life Science and Technology, ShanghaiTech University, Shanghai, PR China
| | - M D Wang
- Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY, United States; Howard Hughes Medical Institute, Cornell University, Ithaca, NY, United States.
| |
Collapse
|
7
|
Ye F, Badman R, Inman JT, Soltani M, Killian JL, Wang MD. Biocompatible and High Stiffness Nanophotonic Trap Array for Precise and Versatile Manipulation. NANO LETTERS 2016; 16:6661-6667. [PMID: 27689302 PMCID: PMC5515237 DOI: 10.1021/acs.nanolett.6b03470] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The advent of nanophotonic evanescent field trapping and transport platforms has permitted increasingly complex single molecule and single cell studies on-chip. Here, we present the next generation of nanophotonic Standing Wave Array Traps (nSWATs) representing a streamlined CMOS fabrication process and compact biocompatible design. These devices utilize silicon nitride (Si3N4) waveguides, operate with a biofriendly 1064 nm laser, allow for several watts of input power with minimal absorption and heating, and are protected by an anticorrosive layer for sustained on-chip microelectronics in aqueous salt buffers. In addition, due to Si3N4's negligible nonlinear effects, these devices can generate high stiffness traps while resolving subnanometer displacements for each trapped particle. In contrast to traditional table-top counterparts, the stiffness of each trap in an nSWAT device scales linearly with input power and is independent of the number of trapping centers. Through a unique integration of microcircuitry and photonics, the nSWAT can robustly trap, and controllably position, a large number of nanoparticles along the waveguide surface, operating in an all-optical, constant-force mode without need for active feedback. By reducing device fabrication cost, minimizing trapping laser specimen heating, increasing trapping force, and implementing commonly used trapping techniques, this new generation of nSWATs significantly advances the development of a high performance, low cost optical tweezers array laboratory on-chip.
Collapse
Affiliation(s)
- Fan Ye
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
- Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853
| | - Ryan Badman
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
| | - James T. Inman
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
- Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853
| | - Mohammad Soltani
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
- Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853
| | - Jessica L. Killian
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
| | - Michelle D. Wang
- Department of Physics – LASSP, Cornell University, Ithaca, New York 14853
- Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853
| |
Collapse
|
8
|
Sen D, Patel G, Patel SS. Homologous DNA strand exchange activity of the human mitochondrial DNA helicase TWINKLE. Nucleic Acids Res 2016; 44:4200-10. [PMID: 26887820 PMCID: PMC4872091 DOI: 10.1093/nar/gkw098] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 02/08/2016] [Indexed: 01/03/2023] Open
Abstract
A crucial component of the human mitochondrial DNA replisome is the ring-shaped helicase TWINKLE-a phage T7-gene 4-like protein expressed in the nucleus and localized in the human mitochondria. Our previous studies showed that despite being a helicase, TWINKLE has unique DNA annealing activity. At the time, the implications of DNA annealing by TWINKLE were unclear. Herein, we report that TWINKLE uses DNA annealing function to actively catalyze strand-exchange reaction between the unwinding substrate and a homologous single-stranded DNA. Using various biochemical experiments, we demonstrate that the mechanism of strand-exchange involves active coupling of unwinding and annealing reactions by the TWINKLE. Unlike strand-annealing, the strand-exchange reaction requires nucleotide hydrolysis and greatly stimulated by short region of homology between the recombining DNA strands that promote joint molecule formation to initiate strand-exchange. Furthermore, we show that TWINKLE catalyzes branch migration by resolving homologous four-way junction DNA. These four DNA modifying activities of TWINKLE: strand-separation, strand-annealing, strand-exchange and branch migration suggest a dual role of TWINKLE in mitochondrial DNA maintenance. In addition to playing a major role in fork progression during leading strand DNA synthesis, we propose that TWINKLE is involved in recombinational repair of the human mitochondrial DNA.
Collapse
Affiliation(s)
- Doyel Sen
- Rutgers University, Robert Wood Johnson Medical School, Department of Biochemistry and Molecular Biology, NJ 08854, USA
| | - Gayatri Patel
- Rutgers University, Robert Wood Johnson Medical School, Department of Biochemistry and Molecular Biology, NJ 08854, USA
| | - Smita S Patel
- Rutgers University, Robert Wood Johnson Medical School, Department of Biochemistry and Molecular Biology, NJ 08854, USA
| |
Collapse
|
9
|
Kaguni LS, Oliveira MT. Structure, function and evolution of the animal mitochondrial replicative DNA helicase. Crit Rev Biochem Mol Biol 2015; 51:53-64. [PMID: 26615986 DOI: 10.3109/10409238.2015.1117056] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The mitochondrial replicative DNA helicase is essential for animal mitochondrial DNA (mtDNA) maintenance. Deleterious mutations in the gene that encodes it cause mitochondrial dysfunction manifested in developmental delays, defects and arrest, limited life span, and a number of human pathogenic phenotypes that are recapitulated in animals across taxa. In fact, the replicative mtDNA helicase was discovered with the identification of human disease mutations in its nuclear gene, and based upon its deduced amino acid sequence homology with bacteriophage T7 gene 4 protein (T7 gp4), a bi-functional primase-helicase. Since that time, numerous investigations of its structure, mechanism, and physiological relevance have been reported, and human disease alleles have been modeled in the human, mouse, and Drosophila systems. Here, we review this literature and draw evolutionary comparisons that serve to shed light on its divergent features.
Collapse
Affiliation(s)
- Laurie S Kaguni
- a Department of Biochemistry and Molecular Biology and Center for Mitochondrial Science and Medicine , Michigan State University , East Lansing , MI , USA .,b Institute of Biosciences and Medical Technology, University of Tampere , Tampere , Finland , and
| | - Marcos T Oliveira
- c Departamento de Tecnologia , Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista "Júlio de Mesquita Filho" , Jaboticabal , Brazil
| |
Collapse
|
10
|
Sun B, Wang MD. Single-molecule perspectives on helicase mechanisms and functions. Crit Rev Biochem Mol Biol 2015; 51:15-25. [DOI: 10.3109/10409238.2015.1102195] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
11
|
Petukh M, Kucukkal TG, Alexov E. On human disease-causing amino acid variants: statistical study of sequence and structural patterns. Hum Mutat 2015; 36:524-534. [PMID: 25689729 DOI: 10.1002/humu.22770] [Citation(s) in RCA: 104] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 02/09/2015] [Indexed: 12/28/2022]
Abstract
Statistical analysis was carried out on large set of naturally occurring human amino acid variations, and it was demonstrated that there is a preference for some amino acid substitutions to be associated with diseases. At an amino acid sequence level, it was shown that the disease-causing variants frequently involve drastic changes in amino acid physicochemical properties of proteins such as charge, hydrophobicity, and geometry. Structural analysis of variants involved in diseases and being frequently observed in human population showed similar trends: disease-causing variants tend to cause more changes in hydrogen bond network and salt bridges as compared with harmless amino acid mutations. Analysis of thermodynamics data reported in the literature, both experimental and computational, indicated that disease-causing variants tend to destabilize proteins and their interactions, which prompted us to investigate the effects of amino acid mutations on large databases of experimentally measured energy changes in unrelated proteins. Although the experimental datasets were linked neither to diseases nor exclusory to human proteins, the observed trends were the same: amino acid mutations tend to destabilize proteins and their interactions. Having in mind that structural and thermodynamics properties are interrelated, it is pointed out that any large change in any of them is anticipated to cause a disease.
Collapse
Affiliation(s)
- Marharyta Petukh
- Department of Physics, Clemson University, Clemson, SC 29642, USA
| | - Tugba G Kucukkal
- Department of Physics, Clemson University, Clemson, SC 29642, USA
| | - Emil Alexov
- Department of Physics, Clemson University, Clemson, SC 29642, USA
| |
Collapse
|
12
|
Towle-Weicksel JB, Cao Y, Crislip LJ, Thurlow DL, Crampton DJ. Chimeric proteins constructed from bacteriophage T7 gp4 and a putative primase-helicase from Arabidopsis thaliana. Mol Biol Rep 2014; 41:7783-95. [PMID: 25098604 DOI: 10.1007/s11033-014-3671-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 07/29/2014] [Indexed: 11/24/2022]
Abstract
An open reading frame from Arabidopsis thaliana, which is highly homologous to the human mitochondrial DNA helicase TWINKLE, was previously cloned, expressed, and shown to have DNA primase and DNA helicase activity. The level of DNA primase activity of this Arabidopsis Twinkle homolog (ATH) was low, perhaps due to an incomplete zinc binding domain (ZBD). In this study, N-terminal truncations of ATH implicate residues 80-102 interact with the RNA polymerase domain (RPD). In addition, chimeric proteins, constructed using domains from ATH and the well-characterized T7 phage DNA primase-helicase gp4, were created to determine if the weak primase activity of ATH could be enhanced. Two chimeric proteins were constructed: ATHT7 contains the ZBD and RPD domains of ATH tethered to the helicase domain of T7, while T7ATH contains the ZBD and RPD domains of T7 tethered to the helicase domain of ATH. Both chimeric proteins were successfully expressed and purified in E. coli, and assayed for traditional primase and helicase activities. T7ATH was able to generate short oligoribonucleotide primers, but these primers could not be cooperatively extended by a DNA polymerase. Although T7ATH contains the ATH helicase domain, it exhibited few of the characteristics of a functional helicase. ATHT7 lacked primase activity altogether and also demonstrated only weak helicase activities. This work demonstrates the importance of interactions between structurally and functionally distinct domains, especially in recombinant, chimeric proteins.
Collapse
Affiliation(s)
- Jamie B Towle-Weicksel
- Gustaf H. Carlson School of Chemistry and Biochemistry, Clark University, 950 Main St., Worcester, MA, 01610, USA,
| | | | | | | | | |
Collapse
|
13
|
Pandey M, Patel SS. Helicase and polymerase move together close to the fork junction and copy DNA in one-nucleotide steps. Cell Rep 2014; 6:1129-1138. [PMID: 24630996 DOI: 10.1016/j.celrep.2014.02.025] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 01/10/2014] [Accepted: 02/16/2014] [Indexed: 01/25/2023] Open
Abstract
By simultaneously measuring DNA synthesis and dNTP hydrolysis, we show that T7 DNA polymerase and T7 gp4 helicase move in sync during leading-strand synthesis, taking one-nucleotide steps and hydrolyzing one dNTP per base-pair unwound/copied. The cooperative catalysis enables the helicase and polymerase to move at a uniformly fast rate without guanine:cytosine (GC) dependency or idling with futile NTP hydrolysis. We show that the helicase and polymerase are located close to the replication fork junction. This architecture enables the polymerase to use its strand-displacement synthesis to increase the unwinding rate, whereas the helicase aids this process by translocating along single-stranded DNA and trapping the unwound bases. Thus, in contrast to the helicase-only unwinding model, our results suggest a model in which the helicase and polymerase are moving in one-nucleotide steps, DNA synthesis drives fork unwinding, and a role of the helicase is to trap the unwound bases and prevent DNA reannealing.
Collapse
Affiliation(s)
- Manjula Pandey
- Department of Biochemistry and Molecular Biology, Rutgers, The State University of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | - Smita S Patel
- Department of Biochemistry and Molecular Biology, Rutgers, The State University of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
| |
Collapse
|
14
|
Abstract
Threading of DNA through the central channel of a replicative ring helicase is known as helicase loading, and is a pivotal event during replication initiation at replication origins. Once loaded, the helicase recruits the primase through a direct protein-protein interaction to complete the initial 'priming step' of DNA replication. Subsequent assembly of the polymerases and processivity factors completes the structure of the replisome. Two replisomes are assembled, one on each strand, and move in opposite directions to replicate the parental DNA during the 'elongation step' of DNA replication. Replicative helicases are the motor engines of replisomes powered by the conversion of chemical energy to mechanical energy through ATP binding and hydrolysis. Bidirectional loading of two ring helicases at a replication origin is achieved by strictly regulated and intricately choreographed mechanisms, often through the action of replication initiation and helicase-loader proteins. Current structural and biochemical data reveal a wide range of different helicase-loading mechanisms. Here we review advances in this area and discuss their implications.
Collapse
Affiliation(s)
- Panos Soultanas
- School of Chemistry, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
| |
Collapse
|