STRUCTURAL AND FUNCTIONAL-ANALYSIS OF THE GLOBULAR DOMAIN IVA OF THE LAMININ ALPHA-1 CHAIN AND ITS IMPACT ON AN ADJACENT RGD SITE

The globular domain IVa (about 250 residues) of the laminin alpha 1 ch ain was obtained in recombinant form from mammalian cell clones. It wa s prepared either with (alpha 11Va-R) or without (alpha IIVa) an adjac ent cell-adhesive RGD site which seems to be masked in laminin-1. The recombinant products could be visualized as globular structures by rot ary shadowing, were resistant to trypsin and shared immunological epit opes with laminin-l, indicating folding into a native structure. Seque nce analysis of pepsin fragments demonstrated the insertion of the glo bular domain into an epidermal growth factor-like scaffold which is ch aracteristic of the extracellular laminin domain IV (L4) module. Only little immunological cross-reaction was found, however, with other L4 modules from perlecan and different laminin isoforms. Fragment alpha 1 1Va-R, but not fragment alpha 11Va, bound to alpha V beta 3 integrin, although to a distinctly lower level than a laminin fragment where the RGD site is fully exposed. The fragments also had no or only little c ell attachment activity. This confirmed previous predictions that the globular domain alpha 11Va masks the RGD site in laminin-l. Domain alp ha 11Va showed, in addition, a weak binding activity for the basement- membrane protein fibulin-1.