Kim D E, Fisher C, Baker D
Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
J Mol Biol. 2000 May 19;298(5):971-84. doi: 10.1006/jmbi.2000.3701.
The 62 residue IgG binding domain of protein L consists of a central alpha-helix packed on a four-stranded beta-sheet formed by N and C-terminal beta-hairpins. The overall topology of the protein is quite symmetric: the beta-hairpins have similar lengths and make very similar interactions with the central helix. Characterization of the effects of 70 point mutations distributed throughout the protein on the kinetics of folding and unfolding reveals that this symmetry is completely broken during folding; the first beta-hairpin is largely structured while the second beta-hairpin and helix are largely disrupted in the folding transition state ensemble. The results are not consistent with a "hydrophobic core first" picture of protein folding; the first beta-hairpin appears to be at least as ordered at the rate limiting step in folding as the hydrophobic core.
L蛋白的62个残基IgG结合结构域由一个中央α螺旋组成，该螺旋堆积在由N端和C端β发夹形成的四链β折叠片上。该蛋白质的整体拓扑结构非常对称：β发夹长度相似，与中央螺旋的相互作用也非常相似。对分布在整个蛋白质中的70个点突变对折叠和去折叠动力学的影响进行表征，结果表明这种对称性在折叠过程中完全被打破；在折叠过渡态系综中，第一个β发夹基本形成结构，而第二个β发夹和螺旋则基本被破坏。这些结果与蛋白质折叠的“疏水核心优先”图景不一致；在折叠的限速步骤中，第一个β发夹似乎至少与疏水核心一样有序。
