Chemical cross‐linking leads to two high molecular mass aggregates of rat α1β1 integrin differing in their conformation but not in their composition

Open Access
Publisher Website
Google Scholar
Abstract
In order to detect protein interactions of the collagen/laminin receptor α 1 β 1 integrin, covalent chemical cross‐linking was performed with the homo‐bifunctional, amine reactive reagents DSS (disuccinimidylsuberate) and DSP (dithiobis(succinimidylpropionate)). After cross‐linking of the 190 kDa rat α 1 integrin subunit, immunoblotting revealed two additional, immunoreactive, high molecular mass complexes (M r 240/290 k). Generation of the 240/290 kDa aggregates depended on the presence of the intact tertiary protein structure. As shown with immunoaffinity purified proteins, the 240/290 kDa aggregates consist exclusively of α 1 and β 1 integrin subunits. No other cross‐linked proteins associated with the α 1 or β 1 subunit were detected. In contrast to the non‐cross‐linkable α 1 β 1 integrin, the 240/290 kDa aggregates presumably represent active forms of the adhesion receptor, because both bound in vitro to collagen I and IV. This ability of α 1 β 1 integrin to cross‐link and produce two additional high molecular mass forms is shared by rat α 9 β 1 integrin. Thus, the cross‐linking approach directly indicates that β 1 integrins occur in different conformations caused by variations in the folding and/or spatial arrangement of their subunits.