Structure of mammalian plasma fetuin-B and its mechanism of selective metallopeptidase inhibition
Structure of mammalian plasma fetuin-B and its mechanism of selective metallopeptidase inhibition
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DOI：
10.1107/s2052252519001568
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发表时间：
2019-03-01
期刊：
影响因子：
3.9
通讯作者：
Gomis-Rueth, F. Xavier
中科院分区：
文献类型：
--
作者：
Cuppari, Anna;Koerschgen, Hagen;Gomis-Rueth, F. Xavier
胎球蛋白-A和胎球蛋白-B是哺乳动物血清中丰富的具有多种功能的蛋白质。胎球蛋白-B是一种高选择性和有效的抑制剂的金属肽酶（MP）的astacin家族，其中包括ovastacin在哺乳动物。通过抑制ovastacin，胎球蛋白B对女性生育力至关重要。胎球蛋白-B的晶体结构被确定为未结合的，并与原型astacin复合，并发现该抑制剂具有串联的半胱氨酸蛋白酶抑制剂型模块（CY 1和CY 2）。它们通过具有刚性二硫键连接的“CPDCP-主干”的暴露接头连接，并且随后是具有很少规则二级结构的C-末端区域（CTR）。CPDCP-主干和CY 2的发夹形成一个二分楔，其插入MP的活性位点裂缝中。这些元件分别占据裂缝的非引发侧和引发侧，但保留特异性口袋，使得抑制剂不被切割。主干中的天冬氨酸阻断了astacin的催化锌，而CY 2发夹通过QWVXGP基序结合。CY 1模块有助于结构完整性，CTR不参与抑制，如使用一组突变体和变体的体外研究所证实的。总的来说，抑制符合一种新的“提高象鼻”的MP机制，这是让人想起单域半胱氨酸蛋白酶抑制剂的目标半胱氨酸肽酶。超过200个来自脊椎动物的序列已被注释为胎球蛋白B，支持其普遍性和生理相关性;因此，从哺乳动物到软骨鱼类都发现了具有保守的CPDCP和QWVXGP衍生基序的序列。因此，升高的象鼻机制可能对于胎球蛋白B的直系同源物抑制astacins通常是有效的。
Mammalian fetuin-A and fetuin-B are abundant serum proteins with pleiotropic functions. Fetuin-B is a highly selective and potent inhibitor of metallopeptidases (MPs) of the astacin family, which includes ovastacin in mammals. By inhibiting ovastacin, fetuin-B is essential for female fertility. The crystal structure of fetuin-B was determined unbound and in complex with archetypal astacin, and it was found that the inhibitor has tandem cystatin-type modules (CY1 and CY2). They are connected by an exposed linker with a rigid, disulfidelinked 'CPDCP-trunk', and are followed by a C-terminal region (CTR) with little regular secondary structure. The CPDCP-trunk and a hairpin of CY2 form a bipartite wedge, which slots into the active-site cleft of the MP. These elements occupy the nonprimed and primed sides of the cleft, respectively, but spare the specificity pocket so that the inhibitor is not cleaved. The aspartate in the trunk blocks the catalytic zinc of astacin, while the CY2 hairpin binds through a QWVXGP motif. The CY1 module assists in structural integrity and the CTR is not involved in inhibition, as verified by in vitro studies using a cohort of mutants and variants. Overall, the inhibition conforms to a novel 'raised-elephant-trunk' mechanism for MPs, which is reminiscent of single-domain cystatins that target cysteine peptidases. Over 200 sequences from vertebrates have been annotated as fetuin-B, underpinning its ubiquity and physiological relevance; accordingly, sequences with conserved CPDCP- and QWVXGP-derived motifs have been found from mammals to cartilaginous fishes. Thus, the raised-elephant-trunk mechanism is likely to be generally valid for the inhibition of astacins by orthologs of fetuin-B.