STRUCTURAL STUDIES OF CANCER-RELATED PROTEINS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。两种依赖Ca2+的半胱氨酸蛋白酶-和-钙蛋白酶-参与各种Ca2+连接的信号通路，但它们对Ca2+的激活需求有显著差异。利用CHESS收集的衍射数据，我们确定了一种类似钙蛋白酶的结构，它具有85%的钙蛋白酶序列（大亚基的前48个和后62个残基来自m-calpain）和低Ca2+需求。之所以使用这种结构，是因为¿-calpain本身的表达水平太低。如预期的那样，¿-like calpain的整体结构与m-calpain非常相似，但在两个方面存在显著差异。与m-calpain相比，在没有Ca2+的情况下，类钙pain中的催化三残基His和Cys更接近；Ca2+结合EF-hand基序的重要部分是无序的和更灵活的。这些结构差异意味着Ca2+ free¿-calpain可能代表部分激活的结构，需要较低的Ca2+浓度来触发其激活

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