Guyer D M, Henderson I R, Nataro J P, Mobley H L
Department of Microbiology and Immunology, and Center for Vaccine Development, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Mol Microbiol. 2000 Oct;38(1):53-66. doi: 10.1046/j.1365-2958.2000.02110.x.
Urinary tract infection (UTI) is a very common extraintestinal infection, and Escherichia coli is by far the most common causative organism. Uropathogenic E. coli possess traits that distinguish them from commensal strains of E. coli, such as secretion systems that allow virulence factors to be targeted to extracytoplasmic compartments. One of at least five characterized secretion mechanisms is the autotransporter system, which involves translocation of a protein across the inner membrane, presumably via the sec system, and across the outer membrane through a beta-barrel porin structure formed by the carboxy-terminus autotransporter domain. We identified a 107 kDa protein that was expressed significantly more often by E. coli strains associated with the clinical syndrome of acute pyelonephritis than by faecal strains (P = 0.029). We isolated the protein from E. coli CFT073, a strain cultured from the blood and urine of a patient with acute pyelonephritis. The N-terminal amino acid sequence showed highest similarity to two known SPATE (serine protease autotransporters of Enterobacteriaceae) proteins, Pet and EspC. Using a 509 bp probe from the 5' region of pet, 10 cosmid clones of an E. coli CFT073 gene library were positive for hybridization. From one cosmid clone, a 7.5 kb EcoRI restriction fragment, which reacted strongly with the probe, was shown to include the entire 3885 bp gene. The predicted 142 kDa protein product possesses the three domains that are typical of SPATE autotransporters: an unusually long signal sequence of 49 amino acids; a 107 kDa passenger domain containing a consensus serine protease active site (GDSGSG); and a C-terminal autotransporter domain of 30 kDa. The protein exhibited serine protease activity and displayed cytopathic activity on VERO primary kidney, HK-2 bladder and HEp-2 cell lines; the name Sat (secreted autotransporter toxin) was derived from these properties. In addition, Sat antibodies were present in the serum of mice infected with E. coli CFT073. Based upon its association with pathogenic isolates, its cytopathic phenotype and its ability to elicit a strong antibody response after infection, we postulate that Sat represents a novel virulence determinant of uropathogenic E. coli.
尿路感染（UTI）是一种非常常见的肠外感染，而大肠杆菌是迄今为止最常见的致病微生物。尿路致病性大肠杆菌具有一些使其区别于共生大肠杆菌菌株的特性，例如分泌系统，该系统可使毒力因子靶向胞质外区室。至少五种已鉴定的分泌机制之一是自转运体系统，它涉及蛋白质穿过内膜（大概是通过sec系统），并通过由羧基末端自转运体结构域形成的β-桶状孔蛋白结构穿过外膜。我们鉴定出一种107 kDa的蛋白质，与粪便菌株相比，与急性肾盂肾炎临床综合征相关的大肠杆菌菌株更常表达该蛋白（P = 0.029）。我们从大肠杆菌CFT073中分离出该蛋白，CFT073是从一名急性肾盂肾炎患者的血液和尿液中培养出的菌株。其N端氨基酸序列与两种已知的SPATE（肠杆菌科丝氨酸蛋白酶自转运体）蛋白Pet和EspC具有最高的相似性。使用来自pet 5'区域的509 bp探针，大肠杆菌CFT073基因文库的10个黏粒克隆杂交呈阳性。从一个黏粒克隆中，一个与探针强烈反应的7.5 kb EcoRI限制性片段被证明包含整个3885 bp的基因。预测的142 kDa蛋白质产物具有SPATE自转运体典型的三个结构域：一个异常长的49个氨基酸的信号序列；一个107 kDa的乘客结构域，包含一个共有丝氨酸蛋白酶活性位点（GDSGSG）；以及一个30 kDa的C端自转运体结构域。该蛋白表现出丝氨酸蛋白酶活性，并在VERO原代肾细胞、HK-2膀胱细胞和HEp-2细胞系上显示出细胞病变活性；Sat（分泌型自转运体毒素）这个名字就是源于这些特性。此外，感染大肠杆菌CFT073的小鼠血清中存在Sat抗体。基于其与致病分离株的关联、其细胞病变表型以及感染后引发强烈抗体反应的能力，我们推测Sat代表尿路致病性大肠杆菌的一种新型毒力决定因素。
