Membrane Complexes Required for Gliding Motility.

对生活在土壤中的细菌黄粘球菌的研究拓宽了我们对原核生物的认识。M. xanthus利用滑翔运动在相对干燥的环境中觅食营养物质，并在缺乏营养物质的情况下形成含有静止孢子的子实体。我们已经发现了大肠杆菌跨膜TolBQRA蛋白复合体的独立同源基因，这些基因对生长过程中的滑行运动至关重要。令人惊讶的是，在发育过程中，Tol蛋白本身并不需要滑行，因为任何Tol基因的破坏都不会影响聚集或子实体的形成。然而，由tol突变体产生的孢子不能成熟，表明tol蛋白在孢子分化的后期阶段是必需的。我们将验证Tol蛋白参与生长过程中滑行运动和孢子成熟过程中所需的生物聚合物运输的假设。Tol复合物功能的重要线索来自于对一个Tol操纵子的研究，即gidA- aglU （tolB1）操纵子。AglU是TolB的同源物，预计是一种外膜脂蛋白。与TolB一样，AglU含有WD-repeat基序，形成b - proprol结构，介导与位于内膜的TolQRA蛋白的蛋白-蛋白相互作用。gidA基因编码大肠杆菌葡萄糖抑制分裂蛋白的同源物，这是一种在许多原核生物中存在的功能未知的蛋白质。纯化的黄原草GidA在450nm处吸收，其特征表明它是一种黄蛋白。gidA突变体不能聚集，细胞不能分化成孢子。此外，gidA突变体释放出一种抑制野生型细胞发育的物质。这种抑制剂很可能通过Tol复合物输出，因为aglU的第二次突变阻止了这种有毒物质的释放。分析从gidA突变体中纯化的抑制剂，可能为通过Tol复合物分泌的物质的性质提供线索。

0094635HartzellStudies of the soil-dwelling bacterium Myxococcus xanthus have broadened our understanding of prokaryotic biology. M. xanthus uses gliding motility to forage for nutrients in relatively dry environments and to form a fruiting body containing quiescent spores in the absence of nutrients. We have discovered independent sets of genes encoding homologs of the E. coli transmembrane TolBQRA protein complex that are essential for gliding motility during growth. Surprisingly, the Tol proteins are not needed for gliding per se during development, because disruption of any of the tol genes does not affect aggregation or fruiting body formation. However, the spores produced by tol mutants fail to mature, showing that the Tol proteins are required at a late stage of spore differentiation. We will test the hypothesis that the Tol proteins are involved in the transport of biopolymers needed for gliding motility during growth and spore maturation during development. Important clues to the function of the Tol complex have come from the study of one tol operon, the gidA- aglU (tolB1) operon. AglU, a homolog of TolB, is predicted to be an outer membrane lipoprotein. Like TolB, AglU contains WD-repeat motifs that form B-propellar structures that mediate protein-protein interactions with the TolQRA proteins located in the inner membrane. The gidA gene encodes a homolog of the E. coli glucose-inhibited division protein, a protein of unknown function present in many prokaryotes. Purified M. xanthus GidA absorbs at 450nm and has features showing that it is a flavoprotein. The gidA mutant does not aggregate and cells do not differentiate into spores. Moreover, the gidA mutant releases a substance that inhibits the development of wild-type cells. The inhibitor is likely exported via the Tol complex, because a second mutation in aglU prevents the release of this toxic substance. Analysis of the inhibitor, purified from the gidA mutant, may provide clues to the nature of the material secreted through the Tol complex.