Effect of Proline mutation on stability of Hup protein in Helicobacter pylori

Abstract

Helicobacter pylori, an infectious agent that colonize the gastric system of humans and cause gastritis, peptic ulcers, and gastric cancer ( Suerbaum& Michetti2002). 50% of humans get infected with H. pylori at childhood stage but remain asymptomatic. Prokaryotes lack well defined jacket organelles, hence no discrete compartmentalized nucleus is available. However, Nucleoid associated proteins (NAPs) facilitate DNA super-coiling in the event of gene regulation and expression ( Jaiswal et al . 2018 ) . Hup is one of the major NAP present in H. pylori and responsible for DNA repair and maintenance. Hup belongs to the HU family ( Histone like DNA binding ) of protein that characteristically exist as homo/ hetero-dimer. The monomer units are generally inter-twined to form dimer (higher-state oligomer in some cases) that comprises of two major domains; Dimerization domain and DNA binding domain, respectively Jaiswal et al . 2018 ( ) . The dimerization domain is integral to protein as it maintains the structural integrity of the protein, whereas DNA binding domain consists of β-sheets forming β-arms that help in mechanical DNA clasping. Evolutionarily, the proline residues in the DNA binding domain are conserved and witness mutation rarely. The major proline residues that may have significant role in DNA binding for Hup are Pro 64, Pro78 and Pro 82. These residues have been reported and hypothesized previously for their inter-calation role. However, no significant report is present, to best of our knowledge, that establishes the adverse effects of proline mutations on stability of Hup protein. Therefore, to test the effect of proline mutations on Hup stability urea denaturation study was performed.