Expression, purification and X-ray crystallographic analysis of the Helicobacter pylori blood group antigen-binding adhesin BabA

Helicobacter pylori is a human pathogen that colonizes about 50% of the world's population, causing chronic gastritis, duodenal ulcers and even gastric cancer. A steady emergence of multiple antibiotic resistant strains poses an important public health threat and there is an urgent requirement for alternative therapeutics. The blood group antigen-binding adhesin BabA mediates the intimate attachment to the host mucosa and forms a major candidate for novel vaccine and drug development. Here, the recombinant expression and crystallization of a soluble BabA truncation (BabA(25-460)) corresponding to the predicted extracellular adhesin domain of the protein are reported. X-ray diffraction data for nanobody-stabilized BabA 25-460 were collected to 2.25 angstrom resolution from a crystal that belonged to space group P2(1), with unit-cell parameters a = 50.96, b = 131.41, c = 123.40 angstrom, alpha = 90.0, beta = 94.8, gamma = 90.0 degrees, and which was predicted to contain two BabA(25-460)-nanobody complexes per asymmetric unit.