title: Structural studies of hen egg-white lysozyme dimer: comparison with monomer.
abstract: A facile method for the formation of covalent bonds between protein molecules is zero length cross-linking. This method enables the formation of cross-links without use of any chemical reagents. Here, we report a cross-linking method for lysozyme and some structural studies as well as catalytic activity assay was performed on lysozyme dimer. The results showed that catalytic activity of lysozyme dimer was the same as monomer. Also, the GdnCl-induced equilibrium unfolding of hen egg-white lysozyme monomer and dimer at pH 2 was studied over a temperature range of 290.7-303.2 K by means of CD spectroscopy. The lack of coincidence between two unfolding curves at 222 and 289 nm in lysozyme dimer was observed, which suggested the existence of intermediate state in unfolding process, while lysozyme monomer showed a single cooperative transition. Thus, the thermodynamic parameters were estimated on the basis of two-state mechanism for lysozyme monomer and three-state one for lysozyme dimer. These results indicated that zero length cross-linking can stabilize the intermediate, so the population of intermediate increased. Our results offer a special opportunity to study the role of intermediates in protein folding mechanisms. In addition thermal unfolding of monomer and dimer in 222 nm was achieved.
authors.affiliation: Department of Biochemistry and Biophysics, Faculty of Basic Science, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran.
authors.forename: Bahman
authors.initials: B
authors.lastname: Maroufi
authors.forename: Bijan
authors.initials: B
authors.lastname: Ranjbar
authors.forename: Khosro
authors.initials: K
authors.lastname: Khajeh
authors.forename: Hossein
authors.initials: H
authors.lastname: Naderi-Manesh
authors.forename: Hashem
authors.initials: H
authors.lastname: Yaghoubi
mesh_terms: D000818:Animals; D002853:Chromatography, Liquid; D002942:Circular Dichroism; D019281:Dimerization; D004527:Egg Proteins / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D009113:Muramidase / Q000737:chemistry*; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet
chemical_list: D004527:Egg Proteins; C421864:hen egg lysozyme; D009113:Muramidase