Zhang O, Forman-Kay J D
Biochemistry Research Division, Hospital for Sick Children, Toronto, Ontario, Canada.
Biochemistry. 1995 May 23;34(20):6784-94. doi: 10.1021/bi00020a025.
The isolated N-terminal Src homology 3 (SH3) domain of Drosophila drk exists in equilibrium between folded and unfolded states in aqueous buffer near neutral pH. Nuclear magnetic resonance spectra recorded on both states simultaneously exhibit an approximate 1:1 ratio of protein conformations. The folded form is similar to other known SH3 structures, especially the N-terminal SH3 domain of the mammalian homologue GRB2. A stretch of sequential amide-amide nuclear Overhauser effect cross-peaks for resonances of the unfolded state is observed in a region corresponding to beta-strands in the folded state. The results suggest that turn-like conformations may be preferentially sampled in the folding pathway for this predominantly beta-structured SH3 domain. In addition, a stable turn at Leu-28 is observed in the unfolded but not in the folded state. Comparison of this unfolded form with a denatured state in 2 M guanidine hydrochloride shows that, while both are highly disordered, these states are not identical and more residual structure is present under nondenaturing conditions.
果蝇drk的分离N端Src同源结构域3（SH3）在接近中性pH的水性缓冲液中，折叠态与未折叠态之间存在平衡。在两种状态下同时记录的核磁共振谱显示，蛋白质构象的比例约为1:1。折叠形式与其他已知的SH3结构相似，尤其是哺乳动物同源物GRB2的N端SH3结构域。在与折叠态β链相对应的区域，观察到了未折叠态共振的一段连续酰胺-酰胺核Overhauser效应交叉峰。结果表明，对于这个主要为β结构的SH3结构域，在折叠途径中可能优先采样类似转角的构象。此外，在未折叠态中观察到Leu-28处有一个稳定的转角，而在折叠态中没有。将这种未折叠形式与2M盐酸胍中的变性态进行比较表明，虽然两者都高度无序，但这些状态并不相同，在非变性条件下存在更多的残余结构。
