Lysozyme degradation by the bovine multicatalytic proteinase complex (proteasome): evidence for a nonprocessive mode of degradation.
Lysozyme degradation by the bovine multicatalytic proteinase complex (proteasome): evidence for a nonprocessive mode of degradation.
复制标题
牛多催化蛋白酶复合物（蛋白酶体）对溶菌酶的降解：非进行性降解模式的证据。
DOI：
10.1021/bi990826h
复制
发表时间：
1999
期刊：
影响因子：
2.9
通讯作者：
Cardozo,C
中科院分区：
文献类型：
--
作者：
Wang,R;Chait,BT;Wolf,I;Kohanski,RA;Cardozo,C
多催化蛋白酶复合体(MPC，Proteasome)由28个亚基组成，排列成四个环，环绕着一个充满水的管道。催化中心面向内管，将蛋白质底物限制在封闭的空间内。利用来自考古细菌的MPC获得的实验结果表明，该复合体对蛋白质的降解是过程的，并导致了降解过程中形成的多肽的长度取决于催化室中活性中心之间的距离的建议。为了测试这些假设对来自高等生物的MPC是否有效，我们使用还原的羧胺甲基化溶菌酶(RCM-Lysozyme)和来自牛脾和脑垂体的MPC检测了蛋白质降解过程中早期和晚期形成的产物的尺寸分布。大多数最终降解产物的长度从6到20个氨基酸不等，对特定的、统一大小的多肽没有明显的偏好。我们的观察表明，裂解位点的选择取决于MPC催化中心的氨基酸序列特异性，而不是活性中心之间的距离。在降解的早期过程中，质量在5到10 kDa之间的多肽在MPC上积累了超过80倍的摩尔过剩，表明大的、部分降解的中间体解离。最初的裂解发生在分子N-末端和C-末端之间的10到44个氨基酸之间，通常涉及从RCM-溶菌酶的N-末端和C-末端去除片段。我们的数据表明，高等生物的MPC对蛋白质的降解涉及一种非过程机制，该机制由多个独立的裂解和降解中间产物的解离组成。讨论了MPC降解蛋白质的一般模型。
The multicatalytic proteinase complex (MPC, proteasome) is composed of 28 subunits organized into four rings surrounding a water-filled canal. The catalytic centers face the inner canal confining protein substrates to an enclosed space. Experimental findings obtained with MPC from archaebacteria suggest that degradation of proteins by the complex is processive and have led to the proposal that the lengths of the peptides formed during degradation depend on the distances between active sites in the catalytic chamber. To test whether these postulates are valid for the MPC from a higher organism, we examined the size distributions of products formed early versus late in the course of protein degradation using reduced carboxamidomethylated lysozyme (RCM-lysozyme) and MPC from bovine spleen and pituitary. The majority of final degradation products ranged in length from 6 to 20 amino acids without a clear predilection for peptides of a particular, uniform size. Our observations suggest that selection of cleavage sites is governed by the amino acid sequence specificity of the MPC catalytic sites rather than the distances between the active sites. Early in the course of degradation, peptides with masses between 5 and 10 kDa accumulated in more than 80-fold molar excess over the MPC, indicating dissociation of large, partially degraded intermediates. Initial cleavages occurred at distances between 10 and 44 amino acids from the N- or C-terminus of the molecule and often involved removal of a fragment from both the N- and C-termini of RCM-lysozyme. Our data indicate that degradation of proteins by MPCs from higher organisms involves a nonprocessive mechanism comprised of multiple, independent cleavages with dissociation of degradation intermediates. A general model for protein degradation by the MPC is discussed.