title: Chaperone-mediated inhibition of tubulin self-assembly.
abstract: Molecular chaperones are known to play an important role in facilitating the proper folding of many newly synthesized proteins. Here, we have shown that chaperone proteins exhibit another unique property to inhibit tubulin self-assembly efficiently. Chaperones tested include alpha-crystallin from bovine eye lenses, HSP16.3, HSP70 from Mycobacterium tuberculosis and alpha (s)-casein from milk. All of them inhibit polymerization in a dose-dependent manner independent of assembly inducers used. The critical concentration of MTP polymerization increases with increasing concentration of HSP16.3. Increase in chaperone concentration lowers the extent of polymerization and increases the lag time of self-assembly reaction. Although the addition of a chaperone at the early stage of elongation phase shows no effect on polymerization, the same concentration of chaperone inhibits polymerization completely when added before the initiation of polymerization. Bindings of HSP16.3 and alpha (s)-casein to tubulin have been confirmed using isothermal titration calorimetry. Affinity constants of tubulin are 5.3 xx 10(4) and 9.8 xx 10(5) M(-1) for HSP16.3 and alpha (s)-casein, respectively. Thermodynamic parameters indicate favourable entropy and enthalpy changes for both chaperones-tubulin interactions. Positive entropy change suggests that the interaction is hydrophobic in nature and desolvation occurring during formation of tubulin-chaperone complex. On the basis of thermodynamic data and observations made upon addition of chaperone at early elongation phase or before the initiation of polymerization, we hypothesize that chaperones bind tubulin at the protein-protein interaction site involved in the nucleation phase of self-assembly.
authors.affiliation: Department of Biochemistry, Bose Institute, Centenary Campus, Calcutta 700054, India.
authors.forename: Gopa
authors.initials: G
authors.lastname: Mitra
authors.forename: Abhik
authors.initials: A
authors.lastname: Saha
authors.forename: Twishasri Das
authors.initials: TD
authors.lastname: Gupta
authors.forename: Asim
authors.initials: A
authors.lastname: Poddar
authors.forename: Kali P
authors.initials: KP
authors.lastname: Das
authors.forename: Sujoy K
authors.initials: SK
authors.lastname: Das Gupta
authors.forename: Bhabatarak
authors.initials: B
authors.lastname: Bhattacharyya
mesh_terms: D001426:Bacterial Proteins / Q000494:pharmacology; D002151:Calorimetry; D002364:Caseins / Q000494:pharmacology; D018833:Chaperonins / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000494:pharmacology; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D018832:Molecular Chaperones / Q000494:pharmacology*; D011108:Polymers / Q000378:metabolism; D013816:Thermodynamics; D014404:Tubulin / Q000737:chemistry* / Q000187:drug effects; D038201:alpha-Crystallins / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D002364:Caseins; D018840:HSP70 Heat-Shock Proteins; C444642:HSP70 protein, Mycobacterium tuberculosis; C431133:Hsp16.3 protein, Mycobacterium tuberculosis; D018832:Molecular Chaperones; D011108:Polymers; D014404:Tubulin; D038201:alpha-Crystallins; D018833:Chaperonins