Crystallization and X-ray analysis of the extracellular adhesion domain of Helicobacter pylori adhesin A: the significance of the cation composition in the crystallization precipitant

Abstract

Adherence to host cells is a crucial step in the process of bacterial infection, which is usually mediated by a number of outer membrane proteins identified as adhesins. Helicobacter pylori adhesin A (HpaA) is a member of the adhesin family that mediates the adherence of Helicobacter pylori to gastric epithelial cells, and consequently assists the bacteria in becoming a life-long colonizer of the human stomach. In this study, two constructs were made for the production of truncated HpaA proteins comprising residues 31-260 and 53-260, respectively. The products of both constructs were crystallized, but only the protein from the shorter construct (residues 53-260) formed crystals that were capable of diffraction. In the subsequent optimization trials, crystals in different forms were unexpectedly obtained by using lithium sulfate and ammonium sulfate as the precipitant. An X-ray data set was collected to 1.95 angstrom resolution on beamline BL18U1 at SSRF using a crystal grown with 1.92 M lithium sulfate, which belonged to space group P6(5) with unit-cell parameters a = b = 95.42, c = 54.72 angstrom, gamma = 120 degrees, while another crystal grown with 1.9 M ammonium sulfate diffracted to 2.60 angstrom resolution and the collected data set was indexed in space group P2(1)2(1)2, with unit-cell parameters a = 121.01, b = 190.56, c = 106.31 angstrom The collection of diffraction data has established a solid basis for structure determination.