STRUCTURAL STUDIES OF CANCER-RELATED PROTEINS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 依赖于钙离子的两种半胱氨酸蛋白酶-和-钙蛋白参与了各种与钙相关的信号通路，但激活所需的钙离子却有很大的不同。利用在CHESS上收集的衍射数据，我们确定了一个类钙蛋白的结构，它含有85%的钙蛋白序列(大亚基的前48个和最后62个残基是来自m-钙蛋白的残基)，对钙的需求很低。之所以使用这种结构，是因为-calain本身表达得太差了。与预期的一样，类钙蛋白的结构在整体折叠上与m-钙蛋白非常相似，但在两个方面有明显的不同。与m-calain相比，类calain中的催化三联体残基His和Cys在无Ca~(2+)的情况下距离更近；与Ca~(2+)结合的EF-Hand基序中的很大一部分是无序的和更灵活的。这些结构上的差异表明，无钙钙蛋白可能代表了部分激活的结构，需要较低的钙离子浓度才能触发其激活

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The two Ca2+-dependent cysteine proteases, ¿- and ¿-calpain, are involved in various Ca2+-linked signal pathways, but differ markedly in their Ca2+ requirements for activation. Using diffraction data collected at CHESS, we have determined the structure of a ¿-like calpain, which has 85% ¿-calpain sequence (the first 48 and the last 62 residues of the large subunit are those from m-calpain) and a low Ca2+ requirement. This construct was used because ¿-calpain itself is too poorly expressed. The structure of ¿-like calpain is very similar in overall fold to that of m-calpain as expected, but differs significantly in two aspects. In comparison with m-calpain, the catalytic triad residues in ¿-like calpain, His and Cys, are much closer together in the absence of Ca2+; and significant portions of the Ca2+-binding EF-hand motifs are disordered and more flexible. These structural differences imply that Ca2+-free ¿-calpain may represent a partially activated structure, requiring lower Ca2+ concentration to trigger its activation