Chemical characterization and functional role of human glomerular basement membrane components

Subfractions of human glomerular basement membrane isolated by enzymatic procedures were analyzed for their chemical structure and biological activity. Pepsin or collagenase digestion of purified basement membranes released three groups of components: collagenous and noncollagenous fractions and also a mixed material consisting of a proteolysis-resistant association between collagen sequences and heteropolysaccharidic glycopeptides. These different fractions were explored in vitro for their ability to interact with cell membranes. In fact, only fractions containing the heterogenous material agglutinated human transformed or embryonic cells within 2 h. The cell agglutination was specifically inhibited by N-acetylosamines and N-acetylneuraminic acid. An additional incubation of 20 h at 37 degrees C of the agglutinated cells, maintained in a minimal medium devoid of serum, led to a morphological change of the transformed cells due to an increased cell adhesion and cell spreading. These experimental data suggest that the basement membrane possesses active sites - consisting of an association between collagen and structural glycoproteins - which could play a primordial role in cell matrix interactions.