Structural basis of Lewis b antigen binding by the Helicobacter pylori adhesin BabA

• Published in: Science advances Vol. 1; no. 7
• Main Authors: Hage, Naim, Howard, Tina, Phillips, Chris, Brassington, Claire, Overman, Ross, Debreczeni, Judit, Gellert, Paul, Stolnik, Snow, Winkler, G. Sebastiaan, Falcone, Franco H.
• Format: Journal Article
• Language: English
• Published: 07.08.2015
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.1500315

X-ray structure of BabA bound to Lewis b reveals molecular interactions used by H. pylori to colonize the gastric mucosa. Helicobacter pylori is a leading cause of peptic ulceration and gastric cancer worldwide. To achieve colonization of the stomach, this Gram-negative bacterium adheres to Lewis b (Le b ) antigens in the gastric mucosa using its outer membrane protein BabA. Structural information for BabA has been elusive, and thus, its molecular mechanism for recognizing Le b antigens remains unknown. We present the crystal structure of the extracellular domain of BabA, from H. pylori strain J99, in the absence and presence of Le b at 2.0- and 2.1-Å resolutions, respectively. BabA is a predominantly α-helical molecule with a markedly kinked tertiary structure containing a single, shallow Le b binding site at its tip within a β-strand motif. No conformational change occurs in BabA upon binding of Le b , which is characterized by low affinity under acidic [ K D (dissociation constant) of ~227 μM] and neutral ( K D of ~252 μM) conditions. Binding is mediated by a network of hydrogen bonds between Le b Fuc1, GlcNAc3, Fuc4, and Gal5 residues and a total of eight BabA amino acids (C189, G191, N194, N206, D233, S234, S244, and T246) through both carbonyl backbone and side-chain interactions. The structural model was validated through the generation of two BabA variants containing N206A and combined D233A/S244A substitutions, which result in a reduction and complete loss of binding affinity to Le b , respectively. Knowledge of the molecular basis of Le b recognition by BabA provides a platform for the development of therapeutics targeted at inhibiting H. pylori adherence to the gastric mucosa.