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 pat hogen. Host cell invasion requires the action of the internalins A (In1A) a nd B (In1B), which are members of a family of listerial cell-surface protei ns. Common to these proteins are three distinctive N-terminal domains that have been shown to direct host cell-specific invasion for In1A and In1B. He re, we present the high-resolution crystal structures of these domains pres ent in In1B and In1H, and show thai they constitute a single "internalin do main". In this internalin domain, a central LRR region is flanked contiguou sly by a truncated EF-hand-like cap and an immunoglobulin (1g)-like fold. T l e extended P-sheet, resulting from the distinctive fusion of the LRR and the Ig-like folds, constitutes an adaptable concave interaction surface, wh ich we propose is responsible for the specific recognition of the host cell ular binding partners during infection. (C) 2001 Academic Press.