Su Shengchang, Stephens Bonnie B, Alexandre Gladys, Farrand Stephen K
Department of Microbiology, University of Illinois at Urbana-Champaign, B103 CLSL, 601 South Goodwin Avenue, Urbana, IL 61801, USA.
Department of Biology, Georgia State University, Atlanta, GA 30303, USA.
Microbiology (Reading). 2006 Apr;152(Pt 4):1197-1207. doi: 10.1099/mic.0.28657-0.
The ATP-dependent Lon (La) protease is ubiquitous in nature and regulates a diverse set of physiological responses in bacteria. In this paper a lon mutant of the alpha-proteobacterium Agrobacterium tumefaciens C58 has been characterized. Unlike lon mutants of Escherichia coli, the lon mutant of A. tumefaciens grows very slowly, is not filamentous and exhibits normal resistance to UV irradiation. The mutant retains motility and chemotaxis, produces apparently normal amounts of exopolysacchride, but displays severe defects in cell morphology, with 80 % of the mutant cells appearing Y-shaped. Lon protease of A. tumefaciens shares high homology with its counterparts in E. coli and in Sinorhizobium meliloti, and functionally complements an E. coli lon mutant for defects in morphology and RcsA-mediated regulation of capsular polysaccharide production. Mutations at sites of Lon(At) corresponding to the ATP-binding site and the active site serine of the E. coli Lon protease abolish complementation of phenotypes of the A. tumefaciens and E. coli lon mutants. The nucleotide sequence upstream of A. tumefaciens lon contains an element similar to the consensus sigma(32) heat-shock promoter of E. coli. Northern and Western blot analyses indicated that expression of lon is induced by elevated temperature, albeit to a much lower level than that of groEL. The lon mutant is highly attenuated for virulence, suggesting that Lon may be required for the proper expression, assembly or function of the VirB/D4-mediated T-DNA transfer system.
ATP 依赖性 Lon（La）蛋白酶在自然界中广泛存在，并调节细菌中的多种生理反应。本文对α-变形菌根癌土壤杆菌 C58 的 lon 突变体进行了表征。与大肠杆菌的 lon 突变体不同，根癌土壤杆菌的 lon 突变体生长非常缓慢，没有丝状形态，并且对紫外线照射表现出正常抗性。该突变体保留了运动性和趋化性，产生的胞外多糖量明显正常，但在细胞形态上表现出严重缺陷，80%的突变细胞呈 Y 形。根癌土壤杆菌的 Lon 蛋白酶与其在大肠杆菌和苜蓿中华根瘤菌中的对应物具有高度同源性，并在形态缺陷和 RcsA 介导的荚膜多糖产生调节方面功能互补大肠杆菌 lon 突变体。根癌土壤杆菌 Lon（At）中与大肠杆菌 Lon 蛋白酶的 ATP 结合位点和活性位点丝氨酸相对应的位点发生突变，消除了根癌土壤杆菌和大肠杆菌 lon 突变体表型的互补作用。根癌土壤杆菌 lon 上游的核苷酸序列包含一个类似于大肠杆菌共有σ（32）热休克启动子的元件。Northern 和 Western 印迹分析表明，lon 的表达受温度升高诱导，尽管其水平远低于 groEL。lon 突变体的毒力高度减弱，这表明 Lon 可能是 VirB/D4 介导的 T-DNA 转移系统正常表达、组装或功能所必需的。
