title: Identification of the beta-dystroglycan binding epitope within the C-terminal region of alpha-dystroglycan.
abstract: Dystroglycan is a receptor for extracellular matrix proteins that plays a crucial role during embryogenesis in addition to adult tissue stabilization. A precursor product of a single gene is post-translationally cleaved to form two different subunits, alpha and beta. The extracellular alpha-dystroglycan is a membrane-associated, highly glycosylated protein that binds to various extracellular matrix molecules, whereas the transmembrane beta-dystroglycan binds, via its cytosolic domain, to dystrophin and many other proteins. alpha- and beta-Dystroglycan interact tightly but noncovalently. We have previously shown that the N-terminal region of beta-dystroglycan, beta-DG(654-750), binds to the C-terminal region of murine alpha-dystroglycan independently from glycosylation. Preparing a series of deleted recombinant fragments and using solid-phase binding assays, the C-terminal sequence of alpha-dystroglycan containing the binding epitope for beta-dystroglycan has been defined more precisely. We found that a region of 36 amino acids, from position 550-585, is required for binding the extracellular region, amino acids 654-750 of beta-dystroglycan. Recently, a dystroglycan-like gene was identified in Drosophila that showed a moderate degree of conservation with vertebrate dystroglycan (31% identity, 48% similarity). Surprisingly, the Drosophila sequence contains a region showing a higher degree of identity and conservation (45% and 66%) that coincides with the 550-585 sequence of vertebrate alpha-dystroglycan. We have expressed this Drosophila dystroglycan fragment and measured its binding to the extracellular region of vertebrate (murine) beta-dystroglycan (Kd = 6 +/- 1 microM). These data confirm the proper identification of the beta-dystroglycan binding epitope and stress the importance of this region during evolution. This finding might help the rational design of dystroglycan-specific binding drugs, that could have important biomedical applications.
authors.affiliation: Center for Receptor Chemistry (CNR) Institute of Chemistry and Clinical Chemistry, Catholic University of Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Sciandra
authors.forename: M
authors.initials: M
authors.lastname: Schneider
authors.forename: B
authors.initials: B
authors.lastname: Giardina
authors.forename: S
authors.initials: S
authors.lastname: Baumgartner
authors.forename: T C
authors.initials: TC
authors.lastname: Petrucci
authors.forename: A
authors.initials: A
authors.lastname: Brancaccio
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism; D049030:Dystroglycans; D000939:Epitopes; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; D000939:Epitopes; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D049030:Dystroglycans