Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
Biochemistry. 2010 Mar 23;49(11):2380-8. doi: 10.1021/bi902051e.
The molecular chaperone SecB binds to hydrophobic sections of unfolded secretory proteins and thereby prevents their premature folding prior to secretion by the translocase of Escherichia coli. Here, we have investigated the effect of the single-residue mutation of leucine 42 to arginine (L42R) centrally positioned in the polypeptide binding pocket of SecB on its chaperonin function. The mutant retains its tetrameric structure and SecA targeting function but is defective in its holdase activity. Isothermal titration calorimetry and single-molecule optical tweezer studies suggest that the SecB(L42R) mutant exhibits a reduced polypeptide binding affinity allowing for partial folding of the bound polypeptide chain rendering it translocation-incompetent.
分子伴侣 SecB 与未折叠分泌蛋白的疏水区段结合，从而防止它们在大肠杆菌的转运体之前过早折叠。在这里，我们研究了位于 SecB 多肽结合口袋中央的亮氨酸 42 突变为精氨酸（L42R）对其伴侣蛋白功能的影响。该突变体保留其四聚体结构和 SecA 靶向功能，但在其持家酶活性上存在缺陷。等温滴定量热法和单分子光镊研究表明，SecB（L42R）突变体表现出降低的多肽结合亲和力，允许结合的多肽链部分折叠，使其易位失活。
