title: Native-like tertiary structure in the Mucor miehei lipase molten globule state obtained at low pH.
abstract: Studies on the acid-induced denaturation of Mucor miehei lipase (E.C. 3.1.1.3) were performed by circular dichroism (CD) spectroscopy, fluorescence emission spectroscopy and binding of hydrophobic dye, 1-anilino 8-naphthalenesulfonic acid (ANS). Acid denaturation of the lipase showed loss of secondary structure and alterations in the tertiary structure in the pH range 4 to 2 and 7 to 2 respectively, suggesting that the lipase exists as an acid-unfolded state approximately pH 2.0. A further decrease in pH (from 2.0 to 1.0) resulted in a second transition, which corresponded to the formation of both secondary and tertiary structures. The acid unfolded state at around pH 2.0 has been characterized by significant loss of secondary structure and a small increase in fluorescence intensity with a blue shift of 2 nm, indicating shift of tryptophan residues to less polar environment. Interestingly, the lipase at pH 1.0 exhibits characteristics of molten globule, such as enhanced binding of hydrophobic dye (ANS), native-like secondary structure and slightly altered tryptophanyl environments. That the molten globule of the lipase at pH 1.0 also possesses native-like tertiary structure is an interesting observation made for this lipase.
authors.affiliation: Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh, India.
authors.forename: Sadaf
authors.initials: S
authors.lastname: Fatima
authors.forename: Basir
authors.initials: B
authors.lastname: Ahmad
authors.forename: Rizwan Hasan
authors.initials: RH
authors.lastname: Khan
mesh_terms: D020106:Acrylamide / Q000378:metabolism; D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D002942:Circular Dichroism; D005456:Fluorescent Dyes / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008049:Lipase / Q000737:chemistry*; D009089:Mucor / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence
chemical_list: D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D005656:Fungal Proteins; D020106:Acrylamide; C027132:1-anilino-8-naphthalenesulfonate; D008049:Lipase