Figure 3. BinAB dimer assembly is weakened by proteolysis.

a, The BinAB dimer shown here manifests the largest intermolecular interface in the crystal. The vertical arrow and lens shaped symbol (black) indicate the position of the pseudo two-fold rotation axis that relates BinA and BinB. The interface extends over all four domains in both molecules. Propeptides (dark blue and dark red) play a substantial role in the interface. b, Sphere representation of the BinAB dimer shows that the canonical carbohydrate modules are accessible, but the receptor binding epitope is not, implying that carbohydrate binding occurs first, and then a conformational change exposes the receptor binding epitope. c, d, e Transformation of the BinAB interface accompanying proteolysis. Panel (c) illustrates the BinAB dimer split apart to reveal the interface. (d), All four subdomains and three propeptides contribute to the BinAB interface. Dashed lines connect select propeptide residues in contact across the dimer interface. (e) Dissociation of the propeptides following proteolysis eliminates 42% of the interface. Dotted lines encompassing white patches mark the interface lost after dissociation of the propeptides. Dashed lines connect select residues remaining in contact across the dimer interface following propeptide dissociation. The TM subdomain is the only subdomain that does not lose contacts after proteolysis.