Singh Shanteri, Hager Martin H, Zhang Changsheng, Griffith Byron R, Lee Min S, Hallenga Klaas, Markley John L, Thorson Jon S
Center for Eukaryotic Structural Genomics, Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1544, USA.
ACS Chem Biol. 2006 Aug 22;1(7):451-60. doi: 10.1021/cb6002898.
The recent discovery of the first "self-sacrifice" mechanism for bacterial resistance to the enediyne antitumor antibiotics, where enediyne-induced proteolysis of the resistance protein CalC inactivates both the highly reactive metabolite and the resistance protein, revealed yet another ingenious bacterial mechanism for controlling reactive metabolites. As reported herein, the first 3D structures of CalC and CalC in complex with calicheamicin (CLM) divulge CalC to be a member of the steroidogenic acute regulatory protein (StAR)-related transfer (START) domain superfamily. In contrast to previous studies of proteins known to bind DNA-damaging natural products ( e.g ., bleomycins, mitomycins, and nine-membered chromoprotein enediynes), this is the first demonstrated involvement of a START domain fold. Consistent with the CalC self-sacrifice mechanism, CLM in complex with CalC is positioned for direct hydrogen abstraction from Gly113 to initiate the oxidative proteolysis-based resistance mechanism. These structural studies also illuminate, for the first time, a small DNA-binding region within CalC that may serve to localize CalC to the enediyne target (DNA). Given the role of START domains in nuclear/cytosolic transport and translocation, this structural study also may implicate START domains as post-endocytotic intracellular chaperones for enediyne-based therapeutics such as MyloTarg.
最近发现了细菌对烯二炔类抗肿瘤抗生素产生耐药性的首个“自我牺牲”机制，即烯二炔诱导抗性蛋白CalC的蛋白水解，使高活性代谢物和抗性蛋白均失活，这揭示了细菌控制活性代谢物的另一种巧妙机制。如本文所报道，CalC以及与加利车霉素（CLM）结合的CalC的首个三维结构表明，CalC是类固醇生成急性调节蛋白（StAR）相关转移（START）结构域超家族的成员。与之前对已知结合DNA损伤天然产物的蛋白质（如博来霉素、丝裂霉素和九元发色蛋白烯二炔）的研究不同，这是首次证明START结构域折叠的参与。与CalC自我牺牲机制一致，与CalC结合的CLM的定位是为了直接从Gly113夺取氢，从而启动基于氧化蛋白水解的抗性机制。这些结构研究还首次揭示了CalC内一个小的DNA结合区域，该区域可能有助于将CalC定位到烯二炔靶点（DNA）。鉴于START结构域在核/胞质运输和易位中的作用，这项结构研究还可能暗示START结构域作为基于烯二炔的治疗药物（如麦罗塔）的胞吞后细胞内伴侣。
