HYR, an extracellular module involved in cellular adhesion and related to the immunoglobulin-like fold

Domains belonging to the immunoglobulin-like fold are responsible for a wid e variety of molecular recognition processes. Here we describe a new family of domains, the HYR family, which is predicted to belong to this fold, and which appears to be involved in cellular adhesion. HYR domains were identi fied in several eukaryotic proteins, often associated with Complement Contr ol Protein (CCP) modules or arranged in multiple copies. Our analysis provi des a sequence and structural basis for understanding the role of these dom ains in interaction mechanisms and leads to further characterization of her etofore undescribed repeated domains with similar folds found in several ba cterial proteins involved in enzymatic activities (some chitinases) or in c ell surface adhesion (streptococcal C-alpha antigen).