CHARACTERIZATION OF THE TYROSINE PHOSPHORYLATION AND DISTRIBUTION OF DYSTROBREVIN ISOFORMS

Dystrobrevin, a member of the dystrophin family of proteins, was initi ally identified as a major tyrosine phosphorylated synaptic protein in the electric organ of Torpedo californica, In this paper, we show tha t the major sites of tyrosine phosphorylation of Torpedo dystrobrevin are within its C-terminus, on Tyr-693 and Tyr-710, Cloning of the mamm alian homologue of dystrobrevin has recently shown that this phosphoty rosine containing tail, or PYCT, is subject to alternative splicing. T o compare the expression and distribution of PYCT- and PYCT+ splice va riants, we generated antibodies against different regions of dystrobre vin, Here we show that the PYCT- isoform of 62 kDa is expressed at hig h levels in all tissues examined. In contrast, PYCT+ isoforms are expr essed primarily in brain and muscle, where they are concentrated at sy napses. Moreover, PYCT+ isoforms associate more tightly with the membr ane and with syntrophin, another synaptically enriched protein, These results suggest that PYCT+ isoforms of dystrobrevin are specialized co mponents of the dystroglycan complex which render the complex sensitiv e to regulation by tyrosine kinases, (C) 1998 Federation of European B iochemical Societies.