Sequence-specific interaction between the disintegrin domain of mouse ADAM3 and murine eggs: Role of beta 1 integrin-associated proteins CD9, CD81, and CD98

ADAM 3 is a sperm surface glycoprotein that has been implicated in sperm-eg g adhesion. Because little is known about the adhesive activity of ADAMs, w e investigated the interaction of ADAM 3 disintegrin domains, made in bacte ria and in insect cells, with murine eggs. Both recombinant proteins inhibi ted sperm-egg binding and fusion with potencies similar to that which we re cently reported for the ADAM 2 disintegrin domain. Alanine scanning mutagen esis revealed a critical importance for the glutamine at position 7 of the disintegrin loop. Fluorescent beads coated with the ADAM 3 disintegrin doma in bound to the egg surface. Bead binding was inhibited by an authentic, bu t not by a scrambled, peptide analog of the disintegrin loop. Bead binding was also inhibited by the function-blocking anti-alpha6 monoclonal antibody (mAb) GoH3, but not by a nonfunction blocking anti-alpha6 mAb, or by mAbs against either the alphav or beta3 integrin subunits. We also present evide nce that in addition to the tetraspanin CD9, two other beta1-integrin-assoc iated proteins, the tetraspanin CD81 as well as the single pass transmembra ne protein CD98 are expressed on murine eggs. Antibodies to CD9 and CD98 in hibited in vitro fertilization and binding of the ADAM 3 disintegrin domain . Our findings are discussed in terms of the involvement of multiple sperm ADAMs and multiple egg beta1 integrin-associated proteins in sperm-egg bind ing and fusion. We propose that an egg surface "tetraspan web" facilitates fertilization and that it may do so by fostering ADAM-integrin interactions .