Comparison between the unfolding rate and structural fluctuations in native lysozyme—effects of denaturants, ligand binding, and intrachain cross‐linking on hydrogen exchange and unfolding kinetics

作者：Shin-ichi Segawa, Katsuya Kume · 发表于：Biopolymers · 年份：1986 · DOI：10.1002/bip.360251012 · 被引用次数：16 · 研究领域：Protein Structure and Dynamics、Crystallography and molecular interactions、Enzyme Structure and Function

Abstract The hydrogen‐exchange reactions of peptide NH groups in lysozyme were studied by the change in the intensity of the amide II band in the ir spectrum. The slowest exchanging hydrogens, which are involved in intramolecular hydrogen bonding, are further divided into two groups at lower temperatures; half of them are exchanged through local unfolding and the other half through major cooperative unfolding. In order to study the correlation of the change in hydrogen‐exchange rates with the change in the unfolding rate constant, we observed the effects of intrachain cross‐linking, the addition of denaturant and ligand binding on the exchange rates through local unfolding. Although the exchange rate through major unfolding is greatly decreased by intrachain cross‐linking between Glu 35 and Trp 108 (1/22000), the exchange rate through local unfolding is only slightly decreased (1/20). Even at higher temperatures, where most intact lysozyme molecules unfold, the folded conformation of cross‐linked lysozyme remains compact, and no intermediate exists in which many side‐chain atoms are packed loosely so that the hydrogen‐exchange reaction occurs rapidly. Neither the addition of 2‐PrOD molecules nor (NAG)3 binding affects the exchange rates through local unfolding. Our experiments confirm that the change in the unfolding rate constant does not correlate with the change in fluctuations in the relatively flexible hydrogen‐bonded structure through which the exchange of peptide hydro...