Piubelli Luciano, Pedotti Mattia, Molla Gianluca, Feindler-Boeckh Susanne, Ghisla Sandro, Pilone Mirella S, Pollegioni Loredano
Department of Biotechnology and Molecular Sciences, University of Insubria, 21100 Varese, Italy.
J Biol Chem. 2008 Sep 5;283(36):24738-47. doi: 10.1074/jbc.M802321200. Epub 2008 Jul 9.
The flavoprotein cholesterol oxidase from Brevibacterium sterolicum (BCO) possesses a narrow channel that links the active center containing the flavin to the outside solvent. This channel has been proposed to serve for the access of dioxygen; it contains at its "bottom" a Glu-Arg pair (Glu-475-Arg-477) that was found by crystallographic studies to exist in two forms named "open" and "closed," which in turn was suggested to constitute a gate functioning in the control of oxygen access. Most mutations of residues that flank the channel have minor effects on the oxygen reactivity. Mutations of Glu-311, however, cause a switch in the basic kinetic mechanism of the reaction of reduced BCO with dioxygen; wild-type BCO and most mutants show a saturation behavior with increasing oxygen concentration, whereas for Glu-311 mutants a linear dependence is found that is assumed to reflect a "simple" second order process. This is taken as support for the assumption that residue Glu-311 finely tunes the Glu-475-Arg-477 pair, forming a gate that functions in modulating the access/reactivity of dioxygen.
来自短杆菌属（Brevibacterium sterolicum）的黄素蛋白胆固醇氧化酶（BCO）拥有一条狭窄通道，该通道将含有黄素的活性中心与外部溶剂相连。有人提出这条通道用于氧气的进入；它在“底部”含有一对Glu-Arg（Glu-475-Arg-477），晶体学研究发现其以两种形式存在，分别命名为“开放”和“封闭”，进而有人认为这构成了一个在控制氧气进入中起作用的门。通道两侧残基的大多数突变对氧反应性影响较小。然而，Glu-311的突变导致还原型BCO与氧气反应的基本动力学机制发生转变；野生型BCO和大多数突变体随着氧气浓度增加呈现饱和行为，而对于Glu-311突变体则发现呈线性依赖关系，这被认为反映了一个“简单”的二级过程。这被视为支持这样一种假设，即残基Glu-311精细调节Glu-475-Arg-477对，形成一个在调节氧气进入/反应性中起作用的门。
