Brunet A P, Huang E S, Huffine M E, Loeb J E, Weltman R J, Hecht M H
Department of Chemistry, Princeton University, New Jersey 08544-1009.
Nature. 1993 Jul 22;364(6435):355-8. doi: 10.1038/364355a0.
The turns joining segments of secondary structure have been proposed to be key elements in dictating the folded structures of native proteins. An alternative view assumes that turns play a passive role and are merely default structures that occur as a consequence of interactions between antiparallel segments of secondary structure, with chain reversal being dictated by the context surrounding the turn and not by the sequence of the turn itself. The solvent-exposure of turns and their tolerance to evolutionary variance suggests that they may have little or no effect on the formation of native structures. Previous investigations have focused on various types of beta-turns that connect antiparallel beta-strands with comparatively little reported on the structural role of interhelical turns. Here we probe the structural importance of such a turn in an antiparallel 4-helix bundle by randomly substituting an interhelical tripeptide in cytochrome b-562 with many different amino-acid sequences. Thirty-one of the resulting substituted proteins were characterized and all of them were shown to fold into stable, native-like structures. These results suggest that this interhelical turn does not does not play a dominant role in determining the folded structure of this antiparallel 4-helix bundle.
连接二级结构片段的转角被认为是决定天然蛋白质折叠结构的关键元件。另一种观点认为，转角起被动作用，仅仅是二级结构反平行片段之间相互作用产生的默认结构，链的反向由转角周围的环境决定，而不是由转角本身的序列决定。转角的溶剂暴露情况及其对进化变异的耐受性表明，它们对天然结构的形成可能几乎没有影响。先前的研究集中在连接反平行β链的各种类型的β转角上，而关于螺旋间转角的结构作用报道较少。在这里，我们通过用许多不同的氨基酸序列随机替换细胞色素b-562中的一个螺旋间三肽，来探究这种转角在反平行四螺旋束中的结构重要性。对得到的31种取代蛋白进行了表征，结果表明它们都折叠成稳定的、类似天然的结构。这些结果表明，这种螺旋间转角在决定这种反平行四螺旋束的折叠结构中并不起主导作用。
