title: Delineation of solution burst-phase protein folding events by encapsulating the proteins in silica gels.
abstract: Many studies have shown that during the early stages of the folding of a protein, chain collapse and secondary structure formation lead to a partially folded intermediate. Thus, direct observation of these early folding events is crucial if we are to understand protein-folding mechanisms. Notably, these events usually manifest as the initial unresolvable signals, denoted the burst phase, when monitored during conventional mixing experiments. However, folding events can be substantially slowed by first trapping a protein within a silica gel with a large water content, in which the trapped native state retains its solution conformation. In this study, we monitored the early folding events involving secondary structure formation of five globular proteins, horse heart cytochrome c, equine β-lactoglobulin, human tear lipocalin, bovine α-lactalbumin, and hen egg lysozyme, in silica gels containing 80% (w/w) water by CD spectroscopy. The folding rates decreased for each of the proteins, which allowed for direct observation of the initial folding transitions, equivalent to the solution burst phase. The formation of each initial intermediate state exhibited single exponential kinetics and Arrhenius activation energies of 14-31 kJ/mol.
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Okabe
authors.forename: Seiichi
authors.initials: S
authors.lastname: Tsukamoto
authors.forename: Kazuo
authors.initials: K
authors.lastname: Fujiwara
authors.forename: Naoya
authors.initials: N
authors.lastname: Shibayama
authors.forename: Masamichi
authors.initials: M
authors.lastname: Ikeguchi
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D002645:Chickens; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism; D005782:Gels; D006736:Horses; D006801:Humans; D055767:Immobilized Proteins / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism; D054835:Lipocalin 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D058428:Silica Gel / Q000737:chemistry*; D012995:Solubility
chemical_list: D030161:Avian Proteins; D004800:Enzymes, Immobilized; D005782:Gels; D055767:Immobilized Proteins; C518443:LCN1 protein, human; D007782:Lactoglobulins; D054835:Lipocalin 1; D050505:Mutant Proteins; D058428:Silica Gel; D045304:Cytochromes c; D007768:Lactalbumin; C421864:hen egg lysozyme; D009113:Muramidase