Structure and Stability of FlgD from the Pathogenic 26695 Strain of Helicobacter pylori

Abstract

Flagellin component D (FlgD) is a hook capping protein involved in the proper structural assembly of bacterial flagella but is not present in the mature flagella. We report here the crystal structure of the truncated form of FlgD from the strain 26695 of Helicobacter pylori (HpFlgD_26695) in the P2 space group at 2.8 A resolution, along with data on protein stability. The structure includes only the central globular part of the protein composed of conserved Fn-III and tudor domains, while the N- and C-terminal regions are absent. This structure, together with the tetragonal crystal structure of HpFlgD_26695 and the monoclinic crystal structure of HpFlgD_G27 reported previously, revealed a different mutual orientation of the two domains in the HpFlgD structures in respect to FlgD from Xanthomonas campestris and Pseudomonas aeruginosa. In addition, investigation of protein stability in solution showed higher protein stability then in other bacterial orthologues reported so far.