Pandyarajan Vijay, Smith Brian J, Phillips Nelson B, Whittaker Linda, Cox Gabriella P, Wickramasinghe Nalinda, Menting John G, Wan Zhu-li, Whittaker Jonathan, Ismail-Beigi Faramarz, Lawrence Michael C, Weiss Michael A
From the Departments of Biochemistry.
the La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia.
J Biol Chem. 2014 Dec 12;289(50):34709-27. doi: 10.1074/jbc.M114.608562. Epub 2014 Oct 10.
Crystallographic studies of insulin bound to fragments of the insulin receptor have recently defined the topography of the primary hormone-receptor interface. Here, we have investigated the role of Phe(B24), an invariant aromatic anchor at this interface and site of a human mutation causing diabetes mellitus. An extensive set of B24 substitutions has been constructed and tested for effects on receptor binding. Although aromaticity has long been considered a key requirement at this position, Met(B24) was found to confer essentially native affinity and bioactivity. Molecular modeling suggests that this linear side chain can serve as an alternative hydrophobic anchor at the hormone-receptor interface. These findings motivated further substitution of Phe(B24) by cyclohexanylalanine (Cha), which contains a nonplanar aliphatic ring. Contrary to expectations, [Cha(B24)]insulin likewise exhibited high activity. Furthermore, its resistance to fibrillation and the rapid rate of hexamer disassembly, properties of potential therapeutic advantage, were enhanced. The crystal structure of the Cha(B24) analog, determined as an R6 zinc-stabilized hexamer at a resolution of 1.5 Å, closely resembles that of wild-type insulin. The nonplanar aliphatic ring exhibits two chair conformations with partial occupancies, each recapitulating the role of Phe(B24) at the dimer interface. Together, these studies have defined structural requirements of an anchor residue within the B24-binding pocket of the insulin receptor; similar molecular principles are likely to pertain to insulin-related growth factors. Our results highlight in particular the utility of nonaromatic side chains as probes of the B24 pocket and suggest that the nonstandard Cha side chain may have therapeutic utility.
胰岛素与胰岛素受体片段结合的晶体学研究最近确定了主要激素 - 受体界面的拓扑结构。在此，我们研究了苯丙氨酸（B24）的作用，它是该界面处一个不变的芳香族锚定基团，也是导致糖尿病的人类突变位点。构建了一系列广泛的B24取代突变体，并测试其对受体结合的影响。尽管长期以来芳香性一直被认为是该位置的关键要求，但发现甲硫氨酸（B24）具有基本接近天然的亲和力和生物活性。分子模拟表明，这种线性侧链可作为激素 - 受体界面处的替代疏水锚定基团。这些发现促使我们进一步用环己基丙氨酸（Cha）取代苯丙氨酸（B24），环己基丙氨酸含有一个非平面脂肪族环。与预期相反，[Cha（B24）]胰岛素同样表现出高活性。此外，它对纤维化的抗性以及六聚体快速解离的速率（具有潜在治疗优势的特性）都得到了增强。Cha（B24）类似物的晶体结构，以分辨率为1.5 Å的R6锌稳定六聚体形式测定，与野生型胰岛素的晶体结构非常相似。非平面脂肪族环呈现两种具有部分占有率的椅式构象，每种构象都重现了苯丙氨酸（B24）在二聚体界面处的作用。总之，这些研究确定了胰岛素受体B24结合口袋内锚定残基的结构要求；类似的分子原理可能也适用于胰岛素相关生长因子。我们的结果特别强调了非芳香族侧链作为B24口袋探针的实用性，并表明非标准的Cha侧链可能具有治疗用途。
