Studies of posttranslational modifications in spiny dogfish myelin basic protein

The objective of this investigation was to determine whether nonmammalian m yelin basic protein contained charge isomers resulting from extensive postt ranslational modifications as seen in mammalian MBP, Four charge isomer com ponents from dogfish MBP have been isolated. These forms arise by phosphory lation and deamidation modifications. Components C1, C2 and C3 have been ch aracterized. We are currently characterizing component C8. Dogfish MBP is l ess cationic than mammalian MBP and has about 50% lower mobility on a basic pH get electrophoresis relative to human and to bovine MBP. The mammalian component C1, which is unmodified, is modified in the dogfish by phosphoryl ation. The reduced electrophoretic mobility is largely attributable to the charge reduction resulting from phosphorylation in serine 72, 83, and 120 o r 121 in C1, and C3. In component C2, two or three phosphate groups were di stributed among residues 134, 138 and 139. It was found that dogfish amino acid residue 30 was a lysine residue and not a glutamate residue as reporte d in the literature.