EXTRACELLULAR INTERACTION OF THE VOLTAGE-DEPENDENT CA2+ CHANNEL ALPHA(2)DELTA AND ALPHA(1) SUBUNITS

The role of the extracellular domain of the voltage-dependent Ca2+ cha nnel alpha(2) delta subunit in assembly with the alpha(1C) subunit was investigated. Transiently transfected tsA201 cells processed the alph a(2) delta subunit properly as disulfide linkages and cleavage sites b etween the alpha(2) and delta subunits were shown to be similar to nat ive channel protein. Coimmunoprecipitation experiments demonstrated th at in the absense of delta subunits, alpha(2) subunits do not assemble with alpha(1) subunits. Furthermore, the transmembrane and cytoplasmi c sequences in delta can be exchanged with those of an unrelated prote in without any effect on the association between the alpha(2) delta an d alpha(1) proteins. Extracellular domains of the alpha(2) delta subun its are also shown to be responsible for increasing the binding affini ty of [H-3]PN200-11- l-5-([H-3]methoxycarbonyl)-pyridine-3-carboxylate ) for the alpha(1C) subunit. Investigation of the corresponding intera ction site on the alpha(1) subunit revealed that although tryptic pept ides containing repeat III of native alpha(1S) subunit remain in assoc iation with the alpha(2) delta subunit during wheat germ agglutinin ch romatography, repeat III by itself is not sufficient for assembly with the alpha(2) delta subunit likely interacts with more than one extrac ellular loop of the alpha(1) subunit.