title: The susceptibility of MAP-2 to proteolytic degradation increases when bound to tubulin.
abstract: During experiments studying dietary effects on phosphorylation/dephosphorylation of MAP-2 we found that incubation of microtubules with alkaline phosphatase resulted in extensive proteolysis of MAP-2 but not of tubulin or Tau proteins. In the absence of tubulin, when microtubule-associated proteins (MAPs) were incubated with alkaline phosphatase, MAP-2 was not proteolyzed. This suggests that binding to tubulin induces a conformational change in MAP-2 which makes it more susceptible to proteolysis. The proteolysis of MAP-2 by alkaline phosphatase was prevented by inhibitors of serine proteases, suggesting that the commercial preparation of the enzyme is contaminated by a serine protease and/or that the enzyme also has a weaker proteolytic activity. In addition, selective proteolysis of MAP-2 can be obtained with the metalloprotease collagenase. Brain homogenates are shown to contain a Ca(2+)-dependent protease which selectively degrades MAP-2 bound to tubulin. These results suggest that selective proteolysis of tubulin-bound MAP-2 could play a role in the regulation of microtubule dynamics in response to extracellular signals.
authors.affiliation: Instituto de Investigaciones Citológicas, Fundación Valenciana de Investigaciones Biomédicas, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Grau
authors.forename: V
authors.initials: V
authors.lastname: Felipo
authors.forename: M D
authors.initials: MD
authors.lastname: Miñana
authors.forename: S
authors.initials: S
authors.lastname: Grisolía
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D014020:Tissue Extracts / Q000494:pharmacology; D014404:Tubulin / Q000378:metabolism*; D016875:tau Proteins / Q000378:metabolism
chemical_list: D008869:Microtubule-Associated Proteins; D014020:Tissue Extracts; D014404:Tubulin; D016875:tau Proteins; D000469:Alkaline Phosphatase; D010447:Peptide Hydrolases