Stoichiometry of microtubule-associated protein (MAP2): tubulin and the localisation of the phosphorylation and cysteine residues along the MAP2 primary sequence

Abstract

The stoichiometry of the dimer between chicken microtubule-associated protein 2 (MAP2) and tubulin was determined by quantitative dodecylsulfate/polyacrylamide gel electrophoresis to be 1:12 mol .cntdot. mol-1, a value equal to the number of phosphorylation sites that can be labeled in vitro. The distribution of these sites along the MAP2 primary sequence was determined by cleaving pre-labeled MAP2 with either .alpha.-chymotrypsin or at the 5 cysteine residues with nitrothiocyanobenzoic acid. The phosphorylation sites lie in 2 clusters: 10 within the known tubulin-binding domain at one end of the primary sequence, and a pair midway along the sequence. The tertiary structure of MAP2 is folded to bring all 12 sites into association with the 2 tubulin dimers.