Mechanisms of Helicase-Catalyzed Dna Unwinding

Lohman, Timothy M.; Bjornson, Keith P.

doi:10.1146/annurev.bi.65.070196.001125

Cited by 732 publications

(593 citation statements)

References 13 publications

Supporting

Mentioning

578

Contrasting

Unclassified

Order By: Relevance

“…Knipper's group (12,15,16) has reported that MCM4, -6, and -7 proteins form a stable complex and that MCM2 protein is more loosely associated with the trimeric form of MCM proteins. My conclusion that a hexamer of MCM4, -6, and -7 has DNA helicase activity is consistent with the findings that several helicases including SV40 T antigen (30) function as a hexamer (31)(32)(33). However, a possibility that protein(s) bound to MCM proteins has intrinsically the DNA helicase activity cannot be ruled out.…”

Section: Fig 3 Protein Cross-linking Of MCM Proteins a The Pooledsupporting

confidence: 79%

A DNA Helicase Activity Is Associated with an MCM4, -6, and -7 Protein Complex

Ishimi

1997

Journal of Biological Chemistry

506

508

View full text Add to dashboard Cite

All six minichromosome maintenance (MCM) proteins have DNA-dependent ATPase motifs in the central domain which is conserved from yeast to mammals. Our group purified MCM protein complexes consisting of MCM2, -4 (Cdc21), -6 (Mis5), and -7 (CDC47) proteins from HeLa cells by using histone-Sepharose column chromatography (Ishimi, Y., Ichinose, S., Omori, A., Sato K., and Kimura, H. (1996) J. Biol. Chem. 271, 24115-24122). The present study revealed that both ATPase activity and DNA helicase activity that displaces oligonucleotides annealed to single-stranded circular DNA are associated with an MCM protein complex. Both ATPase and DNA helicase activities were co-purified with a 600-kDa protein complex that is consisted of equal amounts of MCM4, -6, and -7 proteins. An immunodepletion of the MCM protein complex from the purified fraction using anti-MCM4 antibody resulted in the severe reduction of the DNA helicase activity. Displacement of DNA fragments by the DNA helicase suggested that it migrated along single-stranded DNA in the 3 to 5 direction, and the DNA helicase activity was detected only in the presence of hydrolyzable ATP or dATP. These results suggest that this helicase may be involved in the initiation of DNA replication as a DNA unwinding enzyme.There are at least six MCM 1 proteins that play an essential role in eukaryotic DNA replication as follows: MCM2, -3, -4 (Cdc21), -5, -6 (Mis5), and -7 (CDC47) proteins (see reviews in Refs. 1-3). Genetic evidence suggests that these proteins are required for the initiation of DNA replication in yeast (4, 5). The inactivation of human MCM2 protein with antibody consistently inhibits the initiation of DNA replication (6). Interaction between the MCM proteins has been reported in yeast (4, 7), and the protein complexes containing MCM proteins are detected in Drosophila (8), Xenopus (9), mouse (10, 11), and human cells (12)(13)(14). In human cells, MCM4, -6, and -7 proteins form a stable complex, and MCM2 is loosely associated with this complex (12,15,16). MCM3 and -5 proteins also form a stable complex (10, 13). All six of the MCM proteins contain DNA-dependent ATPase motifs in a central domain that is conserved from yeast to mammals, and these motifs are found in several enzymes that unwind the DNA duplex (17). These findings suggest that MCM protein complexes may be involved in the initiation of DNA replication as an enzyme that unwinds DNA in the origin region. However, DNA helicase activity of MCM proteins has not been reported.MCM proteins bind with chromatin before the initiation of DNA replication and are then released from the chromatin as DNA replication proceeds (18 -20). Our group found that MCM protein complexes containing MCM2, -4, -6, and -7 proteins bound tightly with histone H3 in vitro and were purified to near homogeneity by histone-Sepharose column chromatography (21). In the present study, it is shown that both ATPase and DNA helicase activities are associated with an MCM4, -6, and -7 protein complex. EXPERIMENTAL PROCEDURESPurification of MCM ...

show abstract

Section: Fig 3 Protein Cross-linking Of MCM Proteins a The Pooledsupporting

confidence: 79%

A DNA Helicase Activity Is Associated with an MCM4, -6, and -7 Protein Complex

Ishimi

1997

Journal of Biological Chemistry

506

508

View full text Add to dashboard Cite

show abstract

“…The theoretical limit on efficiency of unwinding is thus 9-12 bp unwound per ATP hydrolysis. Experimentally measured values are typically smaller, usually 0.33-1 bp unwound/ATP hydrolyzed [2]. For PcrA, the measured efficiency of unwinding is approximately 1 bp unwound/ATP [11].…”

Section: Helicase Propertiesmentioning

confidence: 97%

“…The average number of base pairs unwound before the helicase falls off the NA is known as the processivity; measured values for different types of helicases vary from 40 to 30,000 bases unwound [2]. Both the rate and the processivity of a helicase are strongly affected by the presence of accessory proteins as well as solution conditions.…”

Section: Helicase Propertiesmentioning

confidence: 99%

A Motor that Makes Its Own Track: Helicase Unwinding of DNA

Betterton

Jülicher

2003

Phys. Rev. Lett.

View full text Add to dashboard Cite

Helicase opening of double-stranded nucleic acids may be "active" (the helicase directly destabilizes the dsNA to promote opening) or "passive" (the helicase binds ssNA available due to a thermal fluctuation which opens part of the dsNA). We describe helicase opening of dsNA, based on helicases which bind single NA strands and move towards the double-stranded region, using a discrete "hopping" model. The interaction between the helicase and the junction where the double strand opens is characterized by an interaction potential. The form of the potential determines whether the opening is active or passive. We calculate the rate of passive opening for the helicase PcrA, and show that the rate increases when the opening is active. Finally, we examine how to choose the interaction potential to optimize the rate of strand separation. One important result is our finding that active opening can increase the unwinding rate by 7 fold compared to passive opening.

show abstract

“…Table 1 compares solubility free energy increments (SFEI=-RTdlnS 2 /dC 3 ; Eq. 1) for effects of selected Hofmeister salts (and HCl) on solubility of aliphatic and aromatic hydrocarbons (for the complete data set, see Table S1); [2][3][4][5][6][7]33,35 representative data for benzene are shown in Fig. 1A.…”

Section: Analysis Of Salt Effects On Model Compound Solubility Using mentioning

confidence: 99%

“…[1][2][3][4][5] At moderate to high salt concentrations (> 0.1 M), osmotic effects (dependent on the number of ions per formula unit but otherwise nonspecific) and ion-specific effects (traditionally called Hofmeister effects) are most significant, while Coulombic effects (valence-specific but otherwise nonspecific) dominate at relatively low salt concentrations. Processes that expose biopolymer surface to the aqueous salt solution (e.g.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic Origin of Hofmeister Ion Effects

2008

View full text Add to dashboard Cite

Quantitative interpretation and prediction of Hofmeister ion effects on protein processes, including folding and crystallization, have been elusive goals of a century of research. Here, a quantitative thermodynamic analysis, developed to treat noncoulombic interactions of solutes with biopolymer surface and recently extended to analyze the effects of Hofmeister salts on the surface tension of water, is applied to literature solubility data for small hydrocarbons and model peptides. This analysis allows us to obtain a minimum estimate of the hydration b 1 (H 2 O Å −2 ) of hydrocarbon surface and partition coefficients K p characterizing the distribution of salts and salt ions between this hydration water and bulk water. Assuming that Na + and ions of Na 2 SO 4 (the salt giving the largest reduction in hydrocarbon solubility as well as the largest increase in surface tension) are fully excluded from the hydration water at the hydrocarbon surface, we obtain the same b 1 as for air-water surface (∼0.18 H 2 O Å −2 ). Rank orders of cation and anion partition coefficients for nonpolar surface follow the Hofmeister series for protein processes, but are strongly offset for cations in the direction of exclusion (preferential hydration). Assuming a coarse-grained decomposition of water accessible surface area (ASA) into nonpolar, polar amide, and other polar ASA and the same hydration b 1 to interpret peptide solubility increments, we determine salt partition coefficients for amide surface. These partition coefficients are separated into single-ion contributions based on the observation that both Cl − and Na + (also K + ) occupy neutral positions in the middle of the anion and cation Hofmeister series for protein processes. Independent of this assignment, we find that all cations investigated are strongly accumulated at amide surface while most anions are excluded. Ion effects are independent and additive, allowing successful prediction of Hofmeister salt effects on micelle formation and other processes from structural information (ASA).

show abstract

Mechanisms of Helicase-Catalyzed Dna Unwinding

Cited by 732 publications

References 13 publications

A DNA Helicase Activity Is Associated with an MCM4, -6, and -7 Protein Complex

A DNA Helicase Activity Is Associated with an MCM4, -6, and -7 Protein Complex

A Motor that Makes Its Own Track: Helicase Unwinding of DNA

Thermodynamic Origin of Hofmeister Ion Effects

Contact Info

Product

Resources

About