Characterization of densin-180, a new brain-specific synaptic protein of the O-sialoglycoprotein family
We purified an abundant protein of apparent molecular mass 180 kDa from the postsynaptic density fraction of rat forebrain and obtained amino acid sequences of three tryptic peptides generated from the protein. The sequences were used to design a strategy for cloning the cDNA encoding the protein by polymerase chain reaction. The open reading frame of the cDNA encodes a novel protein of predicted molecular mass 167 kDa. We have named the protein densin-180. Antibodies raised against the predicted amino and carboxyl sequences of densin-180 recognize a 180 kDa band on immunoblots that is enriched in the postsynaptic density fraction. Immunocytochemical localization of densin-180 in dissociated hippocampal neuronal cultures shows that the protein is highly concentrated at synapses along dendrites. The message encoding densin-180 is brain specific and is more abundant in forebrain than in cerebellum. The sequence of densin-180 contains 17 leucine-rich repeats, a sialomucin domain, an apparent transmembrane domain, and a PDZ domain. This arrangement of domains is similar to that of several adhesion molecules, in particular GPIbalpha, which mediates binding of platelets to von Willebrand factor. We propose that densin-180 participates in specific adhesion between presynaptic and postsynaptic membranes at glutamatergic synapses.
© 1996 Society for Neuroscience. Received July 18, 1996; revised Aug. 16, 1996; accepted Aug. 19, 1996. This work was supported by National Institutes of Health Grants NS28710 and NS17660 and National Science Foundation Grant GER-9023446 to M.B.K., and by fellowships from National Institutes of Health GMS07616 and Merck Corporation to M.L.A. and from the Del Webb foundation to I.S.M. We thank Kai Zinn for suggesting the cloning strategy, Tetsuichiro Saito for help with designing PCR primers, Randy Paterno for help with initial experiments, Dirk Krapf of the Caltech Biopolymer Analysis Facility for peptide sequences, Frank Asuncion and Leslie Schenker for excellent technical assistance, and Kathleen Branson for help with the preparation of this manuscript.
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