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首页> 外文期刊>Biochemistry >Lysozyme degradation by the bovine multicatalytic proteinase complex (proteasome): evidence for a nonprocessive mode of degradation.
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Lysozyme degradation by the bovine multicatalytic proteinase complex (proteasome): evidence for a nonprocessive mode of degradation.

机译：牛多催化蛋白酶复合物（蛋白酶体）对溶菌酶的降解作用：一种非加工性降解方式的证据。

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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.
机译：多催化蛋白酶复合物（MPC，蛋白酶体）由28个亚单位组成，这些亚单位组织成四个环，围绕着充满水的运河。催化中心面向内管，将蛋白质底物限制在一个封闭的空间内。用MPC从古细菌中获得的实验结果表明复合物对蛋白质的降解是进行性的，并提出了在降解过程中形成的肽的长度取决于催化室中活性位点之间距离的提议。为了测试这些假设是否对来自高等生物的MPC有效，我们使用减少的羧酰胺甲基化溶菌酶（RCM-溶菌酶）和来自牛脾脏和垂体的MPC，检查了蛋白质降解过程中早期形成与晚期形成的产物的大小分布。大多数最终降解产物的长度范围为6至20个氨基酸，而没有明确偏向于特定大小均一的肽。我们的观察结果表明裂解位点的选择受MPC催化位点的氨基酸序列特异性支配，而不是由活性位点之间的距离支配。在降解过程的早期，质量在5至10 kDa之间的肽比MPC积累了80倍以上的摩尔过量，这表明较大的部分降解的中间体会解离。初始切割发生在距分子N或C末端10到44个氨基酸之间的距离处，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，来自高等生物的MPC降解蛋白质涉及一种非加工性机制，该机制包括多个独立的裂解以及降解中间体的解离。讨论了由MPC降解蛋白质的通用模型。

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