Chaperone-like activity of tubulin

Tubulin, a ubiquitous protein of eukaryotic cytoskeleton, is a building block unit of microtubule. Although several cellular processes are known to be mediated through the tubulin-microtubule system, the participation of tubulin or microtubule in protein folding pathway has not yet been reported. Here we show that goat brain tubulin has some functions and features similar to many known molecular chaperones. Substoichiometric amounts of tubulin can suppress the non-thermal and thermal aggregation of a number of unrelated proteins such as insulin, equine liver alcohol dehydrogenase, and soluble eye lens proteins containing β- and γ-crystallins. This chaperone-like activity of tubulin becomes more pronounced as temperature increases. Aging of tubulin solution at 37° C also enhances its chaperone-like activity. Tubulin loses its chaperone-like activity upon removal of its flexible hydrophilic C-terminal tail. These results suggest that both electrostatic and hydrophobic interactions are important in substrate binding by tubulin and that the negatively charged C-terminal tails play a crucial role for its chaperone-like activity

Chaperone-like activity of tubulin. Binding and reactivation of unfolded substrate enzymes

The eukaryotic cytoskeletal protein tubulin is a heterodimer of two subunits, α and β , and is a building block unit of microtubules. In a previous communication we demonstrated that tubulin possesses chaperonelike activities by preventing the stress-induced aggregation of various proteins (Guha, S., Manna, T. K., Das, K. P., and Bhattacharyya, B. (1998) J. Biol. Chem. 273, 30077-30080). As an extension of this observation, we explored whether tubulin, like other known chaperones, also protected biological activity of proteins against thermal stress or increased the yields of active proteins during refolding from a denatured state. We show here that tubulin not only prevents the thermal aggregation of alcohol dehydrogenase and malic dehydrogenase but also protects them from loss of activity. We also show that tubulin prevents the aggregation of substrates during their refolding from a denatured state and forms a stable complex with denatured substrate. The activity of malic dehydrogenase, α -glucosidase, and lactate dehydrogenase during their refolding from urea or guanidium hydrochloride denatured states increased significantly in presence of tubulin compared with that without tubulin. These results suggest that tubulin, in addition to its role in mitosis, cell motility, and other cellular events, might be implicated in protein folding and protection from stress

Particle-yield modification in jet-like azimuthal di-hadron correlations in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The yield of charged particles associated with high-$p_{\rm T}$ trigger particles ($8 < p_{\rm T} < 15$ GeV/$c$) is measured with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jet-like correlation peaks in azimuthal di-hadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta $p_{\rm T}> 3$ GeV/$c$ on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found.Comment: 15 pages, 2 captioned figures, 1 table, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/350

<span style="mso-bidi-language:HI">Purification and characterization of α-amylase from <i>Bacillus amyloliquefaciens</i> <span style="font-size:12.0pt;font-family:"Times New Roman";mso-fareast-font-family: "Times New Roman";mso-bidi-font-family:"Times New Roman";mso-ansi-language: EN-IN;mso-fareast-language:EN-IN;mso-bidi-language:HI">NCIM 2829</span></span>

287-294α-Amylase (EC 3.2.1.1) was purified to homogeneity (specific activity 58,000 µmole min-1 mg protein-1) from the culture filtrate of Bacillus amyloliquefaciens NCIM 2829. Its molecular mass was found to be 67.5 kDa. The activity of the enzyme increased by almost 50% in the presence of Co+2 ion. Hg+2 and Cu+2 acted as strong inhibitors of the enzyme. The tryptophan moities of the enzyme were fairly protected from the aqueous environment. However, the globular interior of the protein was somewhat loosely packed. The protein had nearly an equal amount of α-helical and β-sheet structure in dilute solution. In concentrated solution, its secondary structure had a higher proportion of β-sheet at the expense of some random coil structure. The protein showed a molten globule state at a low concentration of chaotropic agent. The denaturation profile of the protein showed no cooperativity. Co2+ enhanced the structural stability of the enzyme. </span

Surface plasmon resonance study of the interaction of 4,4'-Dianilino-1,1'-binaphthyl-5,5'-disulfonic acid dipotassium salt (bis-ANS) and adenosine triphosphate (ATP) with oligomeric recombinant human lens αA-crystallin

α-crystallin, an abundant mammalian lens protein made up of two subunits (αA- and αB-crystallin), is involved in the maintenance of optimal refractive index in the lens. The protein is implicated in the pathophysiology of a large number of retinal diseases including cataract, age-related macular degeneration, diabetic retinopathy and uveitis. α-crystallin belongs to small heat shock protein (sHSP) family, forms large oligomeric structures, and functions as a molecular chaperone appearing very early during embryonic development. In order to gain mechanistic insight into the structural and functional role of α-crystallin and its alterations in various retinal diseases, it is important to study the interaction chemistry with its known partners. The hydrophobic sites in α-crystallin have been studied extensively using environment sensitive fluorescent probes such as 4,4'-Dianilino-1,1'-binaphthyl-5,5'-disulfonic acid dipotassium salt (bis-ANS) that interacts with both the subunits of α-cystallin in 1:1 stoichiometry at 37oC and diminishes the chaperone-like activity of the protein. Furthermore, it has been shown that ATP plays a crucial role in the association of α-crystallin with substrate proteins. We use surface plasmon resonance (SPR) to monitor the interactions of immobilized oligomeric recombinant αA subunit of human α-crystallin protein with bis-ANS and ATP. We assess the thermodynamic parameters and kinetics of such interactions at various temperatures. Our results indicate that bis-ANS binds to αA-crystallin with higher affinity when compared to ATP while both display fast interaction kinetics.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Chaperone-mediated inhibition of tubulin self-assembly

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 α -crystallin from bovine eye lenses, HSP16.3, HSP70 from Mycobacterium tuberculosis and α -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 α -casein to tubulin have been confirmed using isothermal titration calorimetry. Affinity constants of tubulin are 5.3 &#215; 104 and 9.8 &#215; 105 M-1 for HSP16.3 and &#945; 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

BisANS binding to tubulin: isothermal titration calorimetry and the site-specific proteolysis reveal the GTP-induced structural stability of tubulin

Interactions of bisANS and ANS to tubulin in the presence and absence of GTP were investigated, and the binding and thermodynamic parameters were determined using isothermal titration calorimetry. Like bisANS binding to tubulin, we observed a large number of lower affinity ANS binding sites (N1 = 1.3, K1 = 3.7 &#215; 105 M-1, N2 = 10.5, K2 = 7 &#215; 104/M-1) in addition to 1-2 higher affinity sites. Although the presence of GTP lowers the bisANS binding to both higher and lower affinity sites (N1 = 4.3, N2 = 11.7 in absence and N1 = 1.8, N2 = 3.6 in presence of GTP), the stoichiometries of both higher and lower affinity sites of ANS remain unaffected in the presence of GTP. BisANS-induced structural changes on tubulin were studied using site-specific proteolysis with trypsin and chymotrypsin. Digestion of both &#945; and &#946; tubulin with trypsin and chymotrypsin, respectively, has been found to be very specific in presence of GTP. GTP has dramatic effects on lowering the extent of nonspecific digestion of &#946; tubulin with trypsin and stabilizing the intermediate bands produced from both &#945; and &#946; . BisANS-treated tubulin is more susceptible to both trypsin and chymotrypsin digestion. At higher bisANS concentration (&gt;20 &#956; M) both &#945; and &#946; tubulins are almost totally digestedwith enzymes, indicating bisANS-induced unfolding or destabilization of tubulin structure. Again, the addition of GTP has remarkable effect on lowering the bisANS-induced enhanced digestion of tubulin as well as stabilizing effect on intermediate bands. These results of isothermal titration calorimetry, proteolysis and the DTNB-kinetics data clearly established that the addition of GTP makes tubulin compact and rigid and hence the GTP-induced stabilization of tubulin structure. No such destabilization of tubulin structure has been noticed with ANS, although, like bisANS, ANS possesses a large number of lower affinity binding sites. On the basis of these results, we propose that the unique structure of bisANS, which in absence of GTP can bind tubulin as a bifunctional ligand (through its two ANS moieties), is responsible for the structural changes of tubulin

Use of a small peptide fragment as an inhibitor of insulin fibrillation process: a study by high and low resolution spectroscopy.

A non-toxic, nine residue peptide, NIVNVSLVK is shown to interfere with insulin fibrillation by various biophysical methods. Insulin undergoes conformational changes under certain stress conditions leading to amyloid fibrils. Fibrillation of insulin poses a problem in its long-term storage, reducing its efficacy in treating type II diabetes. The dissociation of insulin oligomer to monomer is the key step for the onset of fibrillation. The time course of insulin fibrillation at 62°C using Thioflavin T fluorescence shows an increase in the lag time from 120 min without peptide to 236 min with peptide. Transmission electron micrographs show branched insulin fibrils in its absence and less inter-fibril association in its presence. Upon incubation at 62°C and pH 2.6, insulin lost some α-helical structure as seen by Fourier transformed infra-red spectroscopy (FT-IR), but if the peptide is added, secondary structure is almost fully maintained for 3 h, though lost partially at 4 h. FT-IR spectroscopy also shows that insulin forms the cross beta structure indicative of fibrils beyond 2 h, but in the presence of the peptide, α-helix retention is seen till 4 h. Both size exclusion chromatography and dynamic light scattering show that insulin primarily exists as trimer, whose conversion to a monomer is resisted by the peptide. Saturation transfer difference nuclear magnetic resonance confirms that the hydrophobic residues in the peptide are in close contact with an insulin hydrophobic groove. Molecular dynamics simulations in conjunction with principal component analyses reveal how the peptide interrupts insulin fibrillation. In vitro hemolytic activity of the peptide showed insignificant cytotoxicity against HT1080 cells. The insulin aggregation is probed due to the inter play of two key residues, Phe(B24) and Tyr(B26) monitored from molecular dynamics simulations studies. Further new peptide based leads may be developed from this nine residue peptide

Novel role of Wag31 in protection of Mycobacteria under oxidative stress

Wag31 of Mycobacterium tuberculosis belongs to the DivIVA family of proteins known to regulate cell morphology in Gram-positive bacteria. Here we demonstrate an unrecognized, novel role of Wag31 in oxidatively stressed mycobacteria. We report the cleavage of penicillin-binding protein 3 (PBP3) by the intramembrane metalloprotease Rv2869c (MSMEG_2579) in oxidatively stressed cells. Amino acids <SUP>102</SUP>A and <SUP>103</SUP>A of PBP3 are required for Rv2869c-mediated cleavage. Wag31<SUB>MTB</SUB>, by virtue of its interaction with PBP3 through amino acid residues <SUP>46</SUP>NSD<SUP>48</SUP>, protects it from oxidative stress-induced cleavage. PBP3 undergoes cleavage in Mycobacterium smegmatis (strain PM2) harbouring wag31(&#916;<SUP>46</SUP>NSD<SUP>48</SUP>) instead of the wild type, with concomitant reduction in ability to withstand oxidative stress. Overexpression of Wag31(&#916;<SUP>46</SUP>NSD<SUP>48</SUP>) attenuates the survival of M. tuberculosis in macrophages with concomitant cleavage of PBP3, and renders the organism more susceptible towards hydrogen peroxide as well as drugs which generate reactive oxygen species, namely isoniazid and ofloxacin. We propose that targeting Wag31 could enhance the activity of mycobactericidal drugs which are known to generate reactive oxygen species