A developmentally regulated glycoprotein complex from Dictyostelium discoideum.

The monoclonal antibody MUD50 recognizes an epitope on a family of developmentally regulated proteins in Dictyostelium discoideum (Alexander, S., Smith, E., Davis, L., Gooley, A., Por, S. B., Browne, L., and Williams, K. L. (1988) Differentiation 38, 82-90). This epitope is an O-linked oligosaccharide that requires the wild-type modB allele for expression. These glycoproteins are structurally diverse. Some are integral membrane proteins, while others are soluble and do not require detergent for solubilization. One of the soluble glycoproteins, PsB, is also recognized by the monoclonal antibody MUD102, which binds to the polypeptide backbone. The antibody recognizes a single 100-kDa band in Western analysis. In this report we demonstrate that the PsB molecule is part of a specific developmentally regulated multiprotein complex containing six different proteins. The complex is held together by both covalent and noncovalent bonds. Interestingly, only the PsB glycoprotein has the MUD50 O-linked oligosaccharide determinant. None of the proteins in the complex is N-glycosylated as assessed by sensitivity to peptide N-glycosidase F. Only one of the complex proteins is heavily phosphorylated. This work establishes the foundation for additional studies on the biosynthesis, processing, and assembly of the O-glycosylated PsB protein.