THE CORE INTERACTION LOOPS AND CORE LOOP COALESCENCE ENERGY IN PROTEIN FOLDING

正如前几年所描述的那样，我们对蛋白质折叠的研究导致了 对假设：(1)以前未知的非共价相互作用 存在于蛋白质的疏水核心中；(2)这种新的相互作用是 放热，并由形成闭合环的接触基团调节 (3)核心环路交互作用是 对小组联系的细节很敏感，因此有能力 对核心组进行排序。 为了更多地了解这种核心循环交互的性质，我们有 全套同系杂化络合物的Kd测定 由马、金枪鱼、酵母iso-1制备的1、2、4和5(总数为) 和念珠菌细胞色素c和热转变的中点 选定络合物的695 nm吸收带。不同的类型 代表多肽链的不同不连续位置。这个 Kd的值被发现根据不同种类的血红素或 使用了脱脂蛋白(或载脂蛋白)或哪种血红素和 使用载脂蛋白(或载脂蛋白)。数据分析与比较 的氨基酸序列，使我们可以指定6个突变 负责KD的变更。此外，相互作用能受 这种突变是非累加性的。这种相互作用的非线性行为 对于核心环路交互是预期的。在影响KD的6个突变中， 发现4个位于紧密通道的核心(见另一 报告)。在过去的几年里，我们又分配了3个折叠单位 细胞色素c除右声道外。我们假设这其中的每一个 折叠单元与核心循环相关联。 此外，目前的证据，结合在 前几年，认为4个核心环路在地面上结合在一起 状态，并在激活时隔离。目前的结果使我们能够 分别计算核心回路的聚结能 常规构象能。计算出的核心环合并 马细胞色素c的能量(24℃时为-5.25千卡/摩尔)占 大约72%的折叠能量。此外，计算出的 核环结合能的微扰(-4.68千卡/摩尔，24 C)度由Ile 9 to Leu和Leu对Met突变的本质解释 马和酵母的折叠能差异--细胞色素c-L异构酶 由E.H.Zuniga和B.T.Nall发现。

As described in the previous years, our studies of protein folding have led to the hypothesis that (1) a previously unknown non-covalent interaction exists in the hydrophobic cores of proteins; (2) this new interaction is exothermic and mediated by the contacting groups which form a closed loop (core interaction loop) in the core; and (3) the core loop interaction is sensitive to the detail of the group contact and therefore has the ability to order the core groups. To know more about the nature of this core loop interaction, we have measured KD for the complete set of homologous and hybrid complexes of type 1, 2, 4 and 5 (64 in total number) prepared from horse, tuna, yeast iso-1 and Candida cytochromes c and the mid point of thermal transition of the 695 nm absorption band for selected complexes. The different types represent the different discontinuity sites of the polypeptide chain. The value for KD was found to vary depending on which species of heme or apogragment (or apoprotein) was used or which combination of heme and apogragments (or apoprotein) was used. Analysis of the data and comparison of the amino acid sequences have allowed us to assign 6 mutations responsible for KD changes. Furthermore, the interaction energy affected by such mutations is non-additive. Such non-linear behavior of the interaction is expected for the core loop interaction. Of the 6 mutations affecting KD, 4 were found to be located in the core of the tight channel (see another report). In the previous years we have assigned 3 more folding units to cytochrome c in addition to the right channel. We assume that each of these folding units are associated with a core loop. Furthermore, the present evidence, combined with the studies in the previous years, suggest that the 4 core loops are coalesced in the ground state and segregated at the activated. The present results have allowed us to calculate the core loop coalescence energy separately from the conventional conformational energy. The calculated core loop coalescence energy (-5.25 kcal/mol at 24 degree C) of horse cytochrome c accounts to approximately 72 per cent of folding energy. Furthermore, the calculated perturbation of the core loop coalescence energy (-4.68 kcal/mol at 24 degree C) by Ile 9 to Leu and Leu 64 to Met mutations essentially explains the difference of folding energy between horse and yeast iso-l-cytochrome c found by E. H. Zuniga and B. T. Nall.