The Mouse VLA-2 Homologue Supports Collagen and Laminin Adhesion but Not Virus Binding

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Abstract
Human VLA-2 (alpha 2 beta 1) mediates cellular adhesion to collagen and laminin and cell attachment by the human pathogen echovirus 1. We report here the cloning, sequencing and functional expression of the mouse VLA-2 alpha subunit homologue. This integrin subunit is closely related to its human counterpart, with 84% amino acid identity between the human and murine proteins. Conserved structural features include an identical number of amino acids, the presence of an I domain, and identity in the number and position of N-linked glycosylation sites and putative divalent cation binding regions. Murine and human alpha 2 show 30% amino acid divergence within the cytoplasmic tail, a difference that can be detected with antisera directed against the C-terminal peptides. Functionally, mouse alpha 2 was capable of mediating cell attachment to collagen and laminin, and responded to both intra- and extracellular signals with changes in its ligand affinity. In contrast, unlike its human homologue, mouse alpha 2 did not promote binding of echovirus 1. Comparison of the primary structure of the homologues leads us to predict that echovirus 1 may bind in the region of the first two thirds of the human alpha 2 I domain, where the sequences are most divergent, whereas more conserved flanking regions, and the conserved terminal one third of the I domain, may be involved in adhesion to collagen and laminin.