Dick L R, Cruikshank A A, Grenier L, Melandri F D, Nunes S L, Stein R L
ProScript, Inc., Cambridge, Massachusetts 02139, USA.
J Biol Chem. 1996 Mar 29;271(13):7273-6. doi: 10.1074/jbc.271.13.7273.
Lactacystin is a Streptomyces metabolite that inhibits cell cycle progression and induces differentiation in a murine neuroblastoma cell line. The cellular target of lactacystin is the 20 S proteasome, also known as the multicatalytic proteinase complex, an essential component of the ubiquitin-proteasome pathway for intracellular protein degradation. In aqueous solution at pH 8, lactacystin undergoes spontaneous hydrolysis to yield N-acetyl-L-cysteine and the inactive lactacystin analog, clasto-lactacystin dihydroxy acid. We have studied the mechanism of lactacystin hydrolysis under these conditions and found that it proceeds exclusively through the intermediacy of the active lactacystin analog, clasto-lactacystin beta-lactone. Conditions that stabilize lactacystin (and thus prevent the transient accumulation of the intermediate beta-lactone) negate the ability of lactacystin to inactivate the proteasome. Together these findings suggest that lactacystin acts as a precursor for clasto-lactacystin beta-lactone and that the latter is the sole species that interacts with the proteasome.
乳胞素是一种链霉菌代谢产物，可抑制小鼠神经母细胞瘤细胞系的细胞周期进程并诱导分化。乳胞素的细胞靶点是20S蛋白酶体，也称为多催化蛋白酶复合物，它是细胞内蛋白质降解的泛素-蛋白酶体途径的重要组成部分。在pH 8的水溶液中，乳胞素会自发水解，生成N-乙酰-L-半胱氨酸和无活性的乳胞素类似物，即裂环乳胞素二羟基酸。我们研究了在这些条件下乳胞素水解的机制，发现它仅通过活性乳胞素类似物裂环乳胞素β-内酯的中间体进行。稳定乳胞素的条件（从而防止中间β-内酯的短暂积累）会消除乳胞素使蛋白酶体失活的能力。这些发现共同表明，乳胞素作为裂环乳胞素β-内酯的前体，而后者是与蛋白酶体相互作用的唯一物种。
