title: Slow solvation dynamics at the active site of an enzyme: implications for catalysis.
abstract: Solvation dynamics at the active site of an enzyme, glutaminyl-tRNA synthetase (GlnRS), was studied using a fluorescence probe, acrylodan, site-specifically attached at cysteine residue C229, near the active site. The picosecond time-dependent fluorescence Stokes shift indicates slow solvation dynamics at the active site of the enzyme, in the absence of any substrate. The solvation dynamics becomes still slower when the substrate (glutamine or tRNA(Gln)) binds to the enzyme. A mutant Y211H-GlnRS was constructed in which the glutamine binding site is disrupted. The mutant Y211H-GlnRS labeled at C229 with acrylodan exhibited significantly different solvent relaxation, thus demonstrating that the slow dynamics is indeed associated with the active site. Implications for catalysis and specificity have been discussed.
authors.affiliation: Department of Biophysics, Bose Institute, P-1/12 CIT Scheme VIIM, Kolkata 700 054, India.
authors.forename: Soumi
authors.initials: S
authors.lastname: Guha
authors.forename: Kalyanasis
authors.initials: K
authors.lastname: Sahu
authors.forename: Durba
authors.initials: D
authors.lastname: Roy
authors.forename: Sudip Kumar
authors.initials: SK
authors.lastname: Mondal
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Roy
authors.forename: Kankan
authors.initials: K
authors.lastname: Bhattacharyya
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002384:Catalysis; D002942:Circular Dichroism; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006862:Hydrogen Sulfide / Q000737:chemistry; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D012343:RNA, Transfer / Q000378:metabolism; D012351:RNA, Transfer, Gln / Q000378:metabolism; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
chemical_list: D012351:RNA, Transfer, Gln; D012997:Solvents; D005973:Glutamine; D014443:Tyrosine; D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases; C020659:glutaminyl-tRNA synthetase; D003545:Cysteine; D006862:Hydrogen Sulfide