Free-thiol Cys331 exposed during activation process is critical for native tetramer structure of cathepsin C (dipeptidyl peptidase I)
Free-thiol Cys331 exposed during activation process is critical for native tetramer structure of cathepsin C (dipeptidyl peptidase I)
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DOI：
10.1110/ps.2910102
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发表时间：
2002-04-01
期刊：
影响因子：
8
通讯作者：
Mares, M
中科院分区：
文献类型：
--
作者：
Horn, M;Baudys, M;Mares, M
成熟的牛组织蛋白酶C（CC）分子由四个相同的单体组成，每个单体经蛋白水解加工成三条链。五个链内二硫化物和三个非配对半胱氨酸残基每个单体进行了鉴定。除了活性位点中的催化Cys 234之外，还表征了游离巯基Cys 331和Cys 424。Cys 424可归类为不可接近的埋藏残留物。Cys 331的选择性修饰导致天然CC四聚体解离成二聚体。CC催化核心的基于3D同源性的模型表明，Cys 331在前组织蛋白酶C活化期间随着活化肽的去除而暴露。该模型进一步表明，暴露的Cys 331被CC特有的表面疏水簇包围，形成二聚体-二聚体相互作用界面。CC二聚体中活性位点的底物/抑制剂识别与天然四聚体中的显著不同。两者合计，提出了一种机制，假设CC四聚体的形成导致每个CC单体单元的内肽酶样活性位点裂缝的位点特异性闭塞。因此，四聚体提供了CC的二肽基肽酶活性的结构基础，通过与同源单体外肽酶组织蛋白酶H和B中发现的那些不同的底物进入限制机制。总之，四聚体形成的机制以及特定的翻译后加工将CC分离在木瓜蛋白酶家族中。
The mature bovine cathepsin C (CC) molecule is composed of four identical monomers, each proteolytically processed into three chains. Five intrachain disulfides and three nonpaired cysteine residues per monomer were identified. Beside catalytic Cys234 in the active site, free-thiol Cys331 and Cys424 were characterized. Cys424 can be classified as inaccessible buried residue. Selective modification of Cys331 results in dissociation of native CC tetramer into dimers. The 3D homology-based model of the CC catalytic core suggests that Cys331 becomes exposed as the activation peptide is removed during procathepsin C activation. The model further shows that exposed Cys331 is surrounded by a surface hydrophobic cluster, unique to CC, forming a dimer-dimer interaction interface. Substrate/inhibitor recognition of the active site in the CC dimer differs significantly from that in the native tetramer. Taken together, a mechanism is proposed that assumes that the CC tetramer formation results in a site-specific occlusion of endopeptidase-like active site cleft of each CC monomeric unit. Thus, tetramerization provides for the structural basis of the dipeptidyl peptidase activity of CC through a substrate access-limiting mechanism different from those found in homologous monomeric exopeptidases cathepsin H and B, In conclusion, the mechanism of tetramer formation as well as specific posttranslational processing segregates CC in the family of papain proteases.