Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, 91125, United States.
ACS Chem Biol. 2011 Oct 21;6(10):1063-8. doi: 10.1021/cb200153g. Epub 2011 Jul 28.
G protein-coupled receptors (GPCRs) contain a number of conserved proline residues in their transmembrane helices, and it is generally assumed these play important functional and/or structural roles. Here we use unnatural amino acid mutagenesis, employing α-hydroxy acids and proline analogues, to examine the functional roles of five proline residues in the transmembrane helices of the D2 dopamine receptor. The well-known tendency of proline to disrupt helical structure is important at all sites, while we find no evidence for a functional role for backbone amide cis-trans isomerization, another feature associated with proline. At most proline sites, the loss of the backbone NH is sufficient to explain the role of the proline. However, at one site, P210(5.50), a substituent on the backbone N appears to be essential for proper function. Interestingly, the pattern in functional consequences that we see is mirrored in the pattern of structural distortions seen in recent GPCR crystal structures.
G 蛋白偶联受体（GPCRs）在其跨膜螺旋中含有许多保守的脯氨酸残基，人们普遍认为这些残基在功能和/或结构上起着重要作用。在这里，我们使用非天然氨基酸诱变，采用 α-羟基酸和脯氨酸类似物，研究了 D2 多巴胺受体跨膜螺旋中五个脯氨酸残基的功能作用。脯氨酸破坏螺旋结构的众所周知的倾向在所有位置都很重要，而我们没有发现与脯氨酸相关的另一个特征，即骨架酰胺顺反异构化的功能作用的证据。在大多数脯氨酸位置，失去骨架 NH 足以解释脯氨酸的作用。然而，在一个位置，P210（5.50），骨架 N 上的取代基似乎对正确的功能是必不可少的。有趣的是，我们看到的功能后果模式反映在最近的 GPCR 晶体结构中观察到的结构扭曲模式。
