title: DNA binding activity of Helicobacter pylori DnaB helicase: the role of the N-terminal domain in modulating DNA binding activities.
abstract: Replicative helicases are major motor proteins essential for chromosomal DNA replication in prokaryotes. Usually hexameric in solution, their DNA binding property must have different roles at stages ranging from the loading onto a branched structure at initiation from the origin to the highly processive translocation during elongation. Here, we have analysed the DNA binding activity of Helicobacter pylori (Hp) replicative helicase, DnaB. The results indicate that while the C-terminal region is important for its DNA binding activity, the N-terminus appears to dampen the protein's affinity for DNA. The masking activity of the N-terminus does not require ATP or hexamerization of HpDnaB and can be overcome by deleting the N-terminus. It can also be neutralized by engaging the N-terminus in an interaction with a partner like the C-terminus of DnaG primase. The inhibitory effect of the N-terminus on DNA binding activity is consistent with the 3D homology model of HpDnaB. Electron microscopy of the HpDnaB-ssDNA complex showed that HpDnaB preferentially bound at the ends of linear ssDNA and translocated along the DNA in the presence of ATP. These results provide an insight into the stimulatory and inhibitory effects of different regions of HpDnaB on DNA binding activities that may be central to the loading and translocation functions of DnaB helicases.
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India.
authors.forename: Ram G
authors.initials: RG
authors.lastname: Nitharwal
authors.forename: Vijay
authors.initials: V
authors.lastname: Verma
authors.forename: Naidu
authors.initials: N
authors.lastname: Subbarao
authors.forename: Santanu
authors.initials: S
authors.lastname: Dasgupta
authors.forename: Nirupam R
authors.initials: NR
authors.lastname: Choudhury
authors.forename: Suman K
authors.initials: SK
authors.lastname: Dhar
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D001665:Binding Sites; D001692:Biological Transport; D002942:Circular Dichroism; D019915:DNA Primase / Q000737:chemistry / Q000378:metabolism; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D053488:DnaB Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D016480:Helicobacter pylori / Q000201:enzymology*; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008968:Molecular Conformation; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D050505:Mutant Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D019915:DNA Primase; D053488:DnaB Helicases