Bioinformatics analysis and biochemical characterisation of ABC transporter-associated periplasmic substrate-binding proteins ModA and MetQ from Helicobacter pylori strain SS1

Abstract The human gastric pathogen Helicobacter pylori relies on the uptake of host-provided nutrients for its proliferation and pathogenicity. ABC transporters that mediate import of small molecules into the cytoplasm of H. pylori employ their cognate periplasmic substrate-binding proteins (SBPs) for ligand capture in the periplasm. The genome of the mouse-adapted strain SS1 of H. pylori encodes eight ABC transporter-associated SBPs, but little is known about their specificity or structure. In this study, we demonstrated that the SBP annotated as ModA binds molybdate (MoO42−, KD = 3.8 nM) and tungstate (WO42−, KD = 7.8 nM). In addition, we showed that MetQ binds D-methionine (KD = 9.5 μM), but not L-methionine, which suggests the existence of as yet unknown pathway for L-methionine uptake. Homology modelling has led to identification of the ligand-binding residues.