Helicase-Primase Interactions and their Structural Studies in Helicobacter Pylori

Abstract

In eubacterial DNA replication initiation complex, two proteins of prime foci are DnaB helicase, a homohexameric motor protein which unwinds duplex DNA, and DnaG primase, a DNA dependent RNA polymerase which synthesizes oligonucleotide primers for DNA replication.In our study we have found the H. pylori DnaB helicase activity being stimulated by H. pylori DnaG primase, suggesting the presence of helicase-primase cohort at replication fork. We have reported the crystal structure of NTD of HpDnaB helicase at 2.2 A resolution. The structural details of NTD besides SPR studies suggest that the linker region between NTD and C-terminal helicase domain plays a vital role in physiological assembly of NTD dimers, and strong interaction with C-terminal domain (CTD) of primase. The sequence analysis of the linker region reveals that they should form four helix bundles. The surface charge distribution on the primase binding surface of NTD's of various helicases shows that the DnaB-DnaG interaction and stability of the complex appears to be charge dependent.Experimental phasing (SAD) was used to solve the crystal structure of HpDnaG primase CTD from 1.7 A diffraction data. The structure is helical in nature like the other two eubacterial DnaG primase CTD structures of Bacillus stearothermophilus and Escherichia coli. Structural comparison suggests that different orientation of helical hairpin in the DnaG primase CTD may play an important role in the regulation of primase activity.