SEA domain proteolysis determines the functional composition of dystroglycan.
Post-translational modifications of the extracellular matrix receptor dystroglycan (DG) determine its functional state, and defects in these modifications are linked to muscular dystrophies and cancers. A prominent feature of DG biosynthesis is a precursor cleavage that segregates the ligand-binding and transmembrane domains into the noncovalently attached alpha- and beta-subunits. We investigate here the structural determinants and functional significance of this cleavage. We show that cleavage of DG elicits a conspicuous change in its ligand-binding activity. Mutations that obstruct this cleavage result in increased capacity to bind laminin, in part, due to enhanced glycosylation of alpha-DG. Reconstitution of DG cleavage in a cell-free expression system demonstrates that cleavage takes place in the endoplasmic reticulum, providing a suitable regulatory point for later processing events. Sequence and mutational analyses reveal that the cleavage occurs within a full SEA (sea urchin, enterokinase, agrin) module with traits matching those ascribed to autoproteolysis. Thus, cleavage of DG constitutes a control point for the modulation of its ligand-binding properties, with therapeutic implications for muscular dystrophies. We provide a structural model for the cleavage domain that is validated by experimental analysis and discuss this cleavage in the context of mucin protein and SEA domain evolution.
Akhavan
Armin
A
California Pacific Medical Center Research Institute, 475 Brannan St., Ste. 220, San Francisco, CA 94107, USA.
Crivelli
Silvia N
SN
Singh
Manisha
M
Lingappa
Vishwanath R
VR
Muschler
John L
JL
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D017124:Conserved Sequence; D049030:Dystroglycans / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007797:Laminin / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment
D007797:Laminin; D021122:Protein Subunits; D049030:Dystroglycans; D010447:Peptide Hydrolases