title: MAP2 prevents protein aggregation and facilitates reactivation of unfolded enzymes.
abstract: It is well established that in addition to its functional role in cell motility, cell division and intracellular transport, cytoskeletal protein tubulin also possesses significant chaperone-like activity. In vitro studies from our laboratory showed that dimeric tubulin can prevent stress induced aggregation of substrate proteins, can resist thermal deactivation of enzymes and can also refold enzymes from their fully denatured state [Manna, T., Sarkar, T., Poddar, A., Roychowdhury, M., Das, K.P. & Bhattacharyya, B. (2001) J. Biol. Chem.276, 39742-39747]. Negative charges of the C-termini of both subunits of tubulin are essential for this chaperone-like property as the deletion of only beta-C-terminus or the binding of a 14-residue basic peptide P2 to the alpha-C-terminus completely abolishes this property [Sarkar, T., Manna, T., Bhattacharyya, S., Mahapatra, P., Poddar, A., Roy, S., Pena, J., Solana, R., Tarazona, R. & Bhattacharyya, B. (2001) Proteins Struct. Funct. Genet.44, 262-269]. Based on these results, one would expect that the microtubular proteins (MTP, tubulin with microtubular-associated proteins, i.e. MAPs bound to the C-terminus) should not possess any chaperone-like activity. To our surprise we noticed excellent chaperone-like activity of MTP. MTP prevents chemical and thermal aggregation of other proteins and can enhance the extent of refolding of fully unfolded substrate enzymes. Because MTP contains tubulin as well as several MAPs bound to the C-termini of tubulin, we fractionated and purified microtubular associated protein 2 (MAP2) and tau using phosphocellulose chromatography. Experiments with purified proteins demonstrated that it is the MAP2 of MTP that exhibits significant chaperone-like activity. This has been shown by the prevention of dithiothreitol-induced aggregation of insulin, thermal aggregation of alcohol dehydrogenase and regain of enzymatic activity during refolding of unfolded substrates. Tau, which shares a homologous C-terminal domain with MAP2, possesses no such activity.
authors.affiliation: Department of Biochemistry, Centenary Campus, PI/12, Bose Institute, CIT Scheme VIIM, Calcutta 700-054, India.
authors.forename: Taradas
authors.initials: T
authors.lastname: Sarkar
authors.forename: Gopa
authors.initials: G
authors.lastname: Mitra
authors.forename: Suvroma
authors.initials: S
authors.lastname: Gupta
authors.forename: Tapas
authors.initials: T
authors.lastname: Manna
authors.forename: Asim
authors.initials: A
authors.lastname: Poddar
authors.forename: Dulal
authors.initials: D
authors.lastname: Panda
authors.forename: Kali P
authors.initials: KP
authors.lastname: Das
authors.forename: Bhabatarak
authors.initials: B
authors.lastname: Bhattacharyya
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D024342:Amino Acids, Acidic / Q000737:chemistry / Q000235:genetics; D000818:Animals; D004789:Enzyme Activation; D005959:Glucosidases / Q000737:chemistry / Q000378:metabolism; D006041:Goats; D007328:Insulin / Q000737:chemistry; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000502:physiology*; D018832:Molecular Chaperones / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000502:physiology; D011485:Protein Binding; D020673:Protein Renaturation / Q000187:drug effects; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence / Q000379:methods; D014357:Trypsin / Q000378:metabolism; D014404:Tubulin / Q000502:physiology; D016875:tau Proteins / Q000502:physiology
chemical_list: D024342:Amino Acids, Acidic; D007328:Insulin; D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D010446:Peptide Fragments; D014404:Tubulin; D016875:tau Proteins; D000426:Alcohol Dehydrogenase; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; D005959:Glucosidases; D014357:Trypsin