PMID:10460148

Citation	Biswas, EE and Biswas, SB (1999) Mechanism of DNA binding by the DnaB helicase of Escherichia coli: analysis of the roles of domain gamma in DNA binding. Biochemistry 38:10929-39
Abstract	We have analyzed the mechanism of single-stranded DNA (ssDNA) binding mediated by the C-terminal domain gamma of the DnaB helicase of Escherichia coli. Sequence analysis of this domain indicated a specific basic region, "RSRARR", and a leucine zipper motif that are likely involved in ssDNA binding. We have carried out deletion as well as in vitro mutagenesis of specific amino acid residues in this region in order to determine their function(s) in DNA binding. The functions of the RSRARR domain in DNA binding were analyzed by site-directed mutagenesis. DnaBMut1, with mutations R(328)A and R(329)A, had a significant decrease in the DNA dependence of ATPase activity and lost its DNA helicase activity completely, indicating the important roles of these residues in DNA binding and helicase activities. DnaBMut2, with mutations R(324)A and R(326)A, had significantly attenuated DNA binding as well as DNA-dependent ATPase and DNA helicase activities, indicating that these residues also play a role in DNA binding and helicase activities. The role(s) of the leucine zipper dimerization motif was (were) determined by deletion analysis. The DnaB Delta 1 mutant with a 55 amino acid C-terminal deletion, which left the leucine zipper and basic DNA binding regions intact, retained DNA binding as well as DNA helicase activities. However, the DnaB Delta 2 mutant with a 113 amino acid C-terminal deletion that included the leucine zipper dimerization motif, but not the RSRARR sequence, lost DNA binding, DNA helicase activities, and hexamer formation. The major findings of this study are (i) the leucine zipper dimerization domain, I(361)-L(389), is absolutely required for (a) dimerization and (b) ssDNA binding; (ii) the base-rich RSRARR sequence is required for DNA binding; (iii) three regions of domain gamma (gamma I, gamma II, and gamma III) differentially regulate the ATPase activity; (iv) there are likely three ssDNA binding sites per hexamer; and (v) a working model of DNA unwinding by the DnaB hexamer is proposed.
Links	PubMed Online version:10.1021/bi990049l
Keywords	Adenosine Triphosphatases/chemistry; Adenosine Triphosphatases/genetics; Adenosine Triphosphatases/metabolism; Amino Acid Sequence; Bacterial Proteins; Base Sequence; Binding Sites/genetics; DNA Helicases/chemistry; DNA Helicases/genetics; DNA Helicases/metabolism; DNA-Binding Proteins/chemistry; DNA-Binding Proteins/genetics; DNA-Binding Proteins/metabolism; Dimerization; DnaB Helicases; Electrophoresis, Polyacrylamide Gel; Enzyme Activation/genetics; Escherichia coli/enzymology; Leucine Zippers/genetics; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Peptide Fragments/chemistry; Peptide Fragments/genetics; Peptide Fragments/metabolism; Protein Structure, Tertiary; Sequence Deletion
edit table

Significance

You can help EcoliWiki by summarizing why this paper is useful

Useful Materials and Methods

You can help Ecoliwiki by describing the useful materials (strains, plasmids, antibodies, etc) described in this paper.

Annotations

<annotationlinks/>

EcoliWiki Links

Add links to pages that link here (e.g. gene, product, method pages)

References

See Help:References for how to manage references in EcoliWiki.