Four isoforms of Microtubule-associated protein 2s
(MAP2a-d) are produced from a single gene in humans by alternative
splicing. These are known to bind actin in vitro (Nishida
et al, 1981; Sattilaro,
1986; Selden &
Pollard, 1983). The region of this family that
binds microtubule also encompasses the actin-binding region. The region is
composed of three or four repeats of about 18aminoacids in length,
contained within which are cAMP dependent protein kinase phosphorylation sites
that have been shown previously to regulate microtubule binding in vitro and
very possibly in vivo (Ozer & Halpain, 2000).
Binding of microtubules appear to be stronger that the interactions with
microfilaments and so in cells, microtubule co-localizations is seen, only when
this interaction is disrupted by phosphorylation can MAP2 be observed in regions
rich in actin and presumably bound by microfilaments (Ozer
& Halpain, 2000). A complication with the
study of MAPs in vivo and their binding microtubules and microfilaments
is mapmodulin, a 31-kDa protein. Mapmodulin binds MAPs via a tubulin-like
domain (Ulitzur et al, 1997).
Ozer, R.S. &
Halpain, S. (2000). "Phosphorylation-dependent localization of
Microtubule-associate protein MAP2c to the actin cytoskeleton." Mol.Biol.Cell
Nishida, E., Kuwaki,
T., & Sakai, H. (1981). "Phosphorylation of microtubule-associated
proteins (MAPs) and pH of the medium control interactions between MAPs and actin
filaments." J.Biochem. 90, 575-578.
Sattilaro, W. (1986). "Interaction of
microtubule-associated protein 2 with actin filaments." Biochemistry
Selden, S.C. & Pollard, T.D. (1983).
"Phosphorylation of microtubule-associated proteins regulates their
interaction with actin filaments." J.Biol.Chem. 258,
Ulitzur, N., Humbert,
M., & Pfeffer, S.R. (1997). "". PNAS 94, 5084-5089.