Microtubule-associated protein 4 (MAP4) is a non-neuronal microtubule-associated protein that promotes microtubule assembly [, ]. It contains a microtubule binding domain (Tau/MAP repeats) that shares homology with neuronal microtubule-associated protein MAP2 and Tau []. It is a ubiquitous heat-stable MAP responsible for stabilisation of microtubules []. Overexpression of MAP4 causes a shift of tubulin dimers to a polymerised fraction and formed dense, stable microtubule networks []. The persistent transcriptional up-regulation of MAP4, cardiac alpha- and beta-tubulinis is linked to the cytoskeletal abnormality during severe pressure overload-induced cardiac hypertrophy [].
The DIPSY domain is characterised by the distinctive D*I*PSY motif at the very C terminus of yeast cell-wall glycoproteins. It appears not to be conserved in any other species, however. In fungi, cell adhesion is required for flocculation, mating and virulence, and is mediated by covalently bound cell wall proteins termed adhesins. Map4, an adhesin required for mating in Schizosaccharomyces pombe, is N-glycosylated and O-glycosylated, and is an endogenous substrate for the mannosyl transferase Oma4p. Map4 has a modular structure with an N-terminal signal peptide, a serine and threonine (S/T)-rich domain that includes nine repeats of 36 amino acids (rich in serine and threonine residues, but lacking glutamines), and a C-terminal DIPSY domain with no glycosyl-phosphatidyl inositol (GPI)-anchor signal. The N-terminal S/T-rich regions, are required for cell wall attachment, but the C-terminal DIPSY domain is required for agglutination and mating in liquid and solid media [].
