Structural homology of microtubule-associated proteins 1 and 2 demonstrated by peptide mapping and immunoreactivity.

The major high molecular weight microtubule-associated polypeptides from hog brain (MAP-1 and MAP-2) were compared by one- and two-dimensional peptide mapping under varied conditions and by immunological techniques. Partial digestion of MAP-1 and MAP-2 with Staphylococcus aureus V8 protease and analysis in one dimension gave rise to very similar peptide maps independent of whether 125I-, 3H-, or 32P-labeled proteins were used. One-dimensional cleavage patterns of significant similarity were also obtained by partial digestion of MAP-1 and MAP-2 using trypsin or chymotrypsin. Furthermore, a pronounced similarity, although clear nonidentity, of MAP-1 and MAP-2 was also revealed after exhaustive digestion of 125I-labeled proteins with S. aureus V8 protease or trypsin followed by analysis of peptides in two dimensions. For immunological comparison, antisera were used that had been raised in rabbits using electrophoretically purified MAP-1 and MAP-2 components as immunogens. As determined by immunoprecipitation, the antiserum raised to MAP-1 was equally reactive with MAP-1 and MAP-2 components, whereas the antiserum to MAP-2 reacted primarily with MAP-2. Indicating the presence of common as well as unique antigenic determinants on MAP-1 and MAP-2, these results, therefore, were in agreement with the peptide mapping data. Implications of these results for biosynthetic mechanisms as well as differential distribution and functions of MAPs in cells are discussed.