Defining the remarkable structural malleability of a bacterial surface protein Rib domain implicated in infection

Significance Proteins attached to the surface of group A and group B streptococcal human pathogens that contain tandemly arrayed Rib domains have been associated with invasive infections and proposed as potential vaccine candidates. Here, we present structures of the Rib domain, both isolated and in tandem. The Rib domain structure is revealed as a rare example of “domain atrophy” from the much more common immunoglobulin-like fold. Tandem Rib domains adopt a head-to-tail arrangement with limited interdomain flexibility, suggesting that the previously observed, and proposed immune evasion-related, variation in Rib domain number is likely to result in differential projection of the N-terminal host colonization domain from the bacterial surface.