Internalins from the human pathogen Listeria monocytogenes combine three distinct folds into a contiguous internalin domain

Listeria monocytogenes is an opportunistic, food-borne human and animal pathogen. Host cell invasion requires the action of the internalins A (In1A) and B (In1B), which are members of a family of listerial cell-surface proteins. Common to these proteins are three distinctive N-terminal domains that have been shown to direct host cell-specific invasion for In1A and In1B. Here, we present the high-resolution crystal structures of these domains present in In1B and In1H, and show thai they constitute a single internalin domain. In this internalin domain, a central LRR region is flanked contiguously by a truncated EF-hand-like cap and an immunoglobulin (1g)-like fold. Tl e extended P-sheet, resulting from the distinctive fusion of the LRR and the Ig-like folds, constitutes an adaptable concave interaction surface, which we propose is responsible for the specific recognition of the host cellular binding partners during infection. (C) 2001 Academic Press.