β1 integrin subunit dimerization via disulfide bonds

Abstract

Integrins of the β1 family were isolated from human smooth muscle. SDS-PAGE analysis and subsequent immunoblotting demonstrated that integrin samples contain a protein immunologically related to β1 integrin subunit with the previously undescribed apparent molecular mass 205 kD. One-dimensional peptide mapping showed that the 205 kD protein is not a novel β1 related integrin subunit, but a β1 integrin subunit dimer. After reduction the major part of the β1 immunoreactive material migrated from the 205 kD to 130 kD region, indicating that β1 integrin subunit dimers were formed via disulfide bonds. When electrophoretically pure β1 monomer and dimer forms were analized it was found that during SDS-PAGE about 30% of β1 integrin subunit monomers were organized into dimers while approximately 70% of the β1 dimer form was partly disrupted into monomers. It was suggested that this steady-state process is a result of a reversible reaction between intra- and intermolecular disulfide bonds. Possible in vivo dimerization of integrins via disulfide bonds is discussed.