Helicobacter pylori helicase loader protein Hp0897 shows unique functions of N- and C-terminal regions

Abstract

Helicase loaders are required for the loading of helicases at the vicinity of replication origins. In Helicobacter pylori, Hp0897 has been shown to be a potential helicase loader for replicative helicase (HpDnaB) although it does not show any sequence homology with conventional DnaC like helicase loader proteins. Therefore, it is important to investigate the in vivo role of Hp0897 and structure-function analysis with respect to domain mapping of Hp0897 and HpDnaB. Although HporiC is divided into oriC1 and oriC2, the latter has been assigned as functional origin based on loading of initiator protein HpDnaA. Using chromatin immunoprecipitation (ChIP) experiment, we show preferential binding of Hp0897 at oriC2 over oriC1 like HpDnaA highlighting its helicase loader function in vivo. Furthermore, we generated series of deletion mutants for HpDnaB and Hp0897 that enabled us to map the domains of interaction between these two proteins. Interestingly, the C-terminal domain of Hp0897 (Hp0897CTD) shows stronger interaction with HpDnaB over the N-terminal region of Hp0897 (Hp0897NTD). Similar to the full-length protein, Hp0897CTD also stimulates the DNA binding activity of HpDnaB. Furthermore, overexpression of Hp0897 full-length protein in H. pylori leads to an elongated cell phenotype. While the overexpression of Hp0897CTD does not show a phenotype of cell elongation, overexpression of Hp0897NTD shows extensive cell elongation. These results highlight the possible role of Hp0897CTD in helicase loading and Hp0897NTD's unique function linked to cell division that make Hp0897 as a potential drug target against H. pylori.

Keywords: helicobacter pylori; DNA binding; DnaB helicase; cell elongation; helicase loader; origin of replication.