title: pH-induced structural change of a multi-tryptophan protein MPT63 with immunoglobulin-like fold: identification of perturbed tryptophan residue/residues.
abstract: The structural change of M. tuberculosis MPT63, which is predominantly a β-sheet protein having an immunoglobulin like fold, has been investigated in the pH range 7.5-1.5 using various biophysical techniques along with low-temperature phosphorescence (LTP) spectroscopy. MPT63 contains four Tryptophan (Trp) residues at 26, 48, 82, and 129. Although circular dichroism, steady-state and time-resolved fluorescence, time-resolved anisotropy, 1-aniline-8-naphthalene sulfonic (ANS) acid binding, and analytical ultracentrifuge depict more open largely unfolded structure of MPT63 at pH 1.5 and also more accessible nature of Trp residues to neutral quencher at pH 1.5, it is, however, not possible to assign the specific Trp residue/residues being perturbed. This problem has been resolved using LTP of MPT63, which shows optically resolved four distinct (0, 0) bands corresponding to four Trp residues in the pH range 7.5-3.0. LTP at pH 1.5 clearly reveals that the solvent-exposed Trp 82 and the almost buried Trp 129 are specifically affected compared with Trp 48 and Trp 26. Lys 8 and Lys 27 are predicted to affect Trp 129. Tyrosine residues are found to be silent even at pH 1.5. This type of specific perturbation in a multi-Trp protein has not been addressed before. LTP further indicates that partially exposed Trp 48 is preferentially quenched by acrylamide compared with other Trp residues at both pH 7.5 and 1.5. The solvent-exposed Trp 82 is surprisingly found to be not quenched by acrylamide at pH 7.5. All the results are obtained using micromolar concentration of protein and without using any Trp-substituted mutant.
authors.affiliation: a Department of Chemistry , Presidency University , Kolkata 700 073 , India.
authors.forename: Manini
authors.initials: M
authors.lastname: Mukherjee
authors.forename: Ranendu
authors.initials: R
authors.lastname: Ghosh
authors.forename: Krishnananda
authors.initials: K
authors.lastname: Chattopadhyay
authors.forename: Sanjib
authors.initials: S
authors.lastname: Ghosh
mesh_terms: D020106:Acrylamide / Q000737:chemistry; D020816:Amino Acid Motifs; D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D052160:Benzothiazoles; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005456:Fluorescent Dyes; D015870:Gene Expression; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007136:Immunoglobulins / Q000737:chemistry; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D013050:Spectrometry, Fluorescence / Q000379:methods; D055672:Static Electricity; D013816:Thermodynamics; D013844:Thiazoles; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D007136:Immunoglobulins; C103339:MPT63 antigen, Mycobacterium tuberculosis; D011994:Recombinant Proteins; D013844:Thiazoles; D020106:Acrylamide; C009462:thioflavin T; D014443:Tyrosine; C027132:1-anilino-8-naphthalenesulfonate; D014364:Tryptophan
keywords: acid unfolding; correlation time; fluorescence quenching; molten globules; protein folding