Midwest Center for Structural Genomics and Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439.
Department of Chemistry and Biochemistry, University of Berne, Freiestrasse 3, 3012 Berne, Switzerland.
J Biol Chem. 2009 Dec 25;284(52):36670-36679. doi: 10.1074/jbc.M109.062679. Epub 2009 Oct 19.
Many bacteria express phosphoenolpyruvate-dependent phosphotransferase systems (PTS). The mannitol-specific PTS catalyze the uptake and phosphorylation of d-mannitol. The uptake system comprises several genes encoded in the single operon. The expression of the mannitol operon is regulated by a proposed transcriptional factor, mannitol operon repressor (MtlR) that was first studied in Escherichia coli. Here we report the first crystal structures of MtlR from Vibrio parahemeolyticus (Vp-MtlR) and its homolog YggD protein from Shigella flexneri (Sf-YggD). MtlR and YggD belong to the same protein family (Pfam05068). Although Vp-MtlR and Sf-YggD share low sequence identity (22%), their overall structures are very similar, representing a novel all alpha-helical fold, and indicate similar function. However, their lack of any known DNA-binding structural motifs and their unfavorable electrostatic properties imply that MtlR/YggD are unlikely to bind a specific DNA operator directly as proposed earlier. This structural observation is further corroborated by in vitro DNA-binding studies of E. coli MtlR (Ec-MtlR), which detected no interaction of Ec-MtlR with the well characterized mannitol operator/promoter region. Therefore, MtlR/YggD belongs to a new class of transcription factors in bacteria that may regulate gene expression indirectly as a part of a larger transcriptional complex.
许多细菌表达磷酸烯醇丙酮酸依赖性磷酸转移酶系统 (PTS)。甘露醇特异性 PTS 催化 D-甘露醇的摄取和磷酸化。摄取系统由几个基因编码，这些基因编码在单个操纵子中。甘露醇操纵子的表达受一种假定的转录因子甘露醇操纵子阻遏物 (MtlR) 调控，该因子最初在大肠杆菌中进行了研究。在这里，我们报告了来自副溶血性弧菌 (Vp-MtlR) 的 MtlR 和其来自福氏志贺菌 (Sf-YggD) 的同源物 YggD 蛋白的第一个晶体结构。MtlR 和 YggD 属于同一蛋白家族 (Pfam05068)。尽管 Vp-MtlR 和 Sf-YggD 序列同一性较低 (22%)，但它们的整体结构非常相似，代表一种新的全α-螺旋折叠，并表明具有相似的功能。然而，它们缺乏任何已知的 DNA 结合结构基序和不利的静电特性表明，MtlR/YggD 不太可能像之前提出的那样直接结合特定的 DNA 操纵子。这种结构观察进一步得到了大肠杆菌 MtlR (Ec-MtlR) 体外 DNA 结合研究的证实，该研究未检测到 Ec-MtlR 与经过充分表征的甘露醇操纵子/启动子区域的相互作用。因此，MtlR/YggD 属于细菌中一类新的转录因子，它们可能作为更大转录复合物的一部分间接调节基因表达。
