Li X, Johnson D E, Mobley H L
Department of Microbiology and Immunology, University of Maryland, Baltimore, Maryland 21201, USA.
Infect Immun. 1999 Jun;67(6):2822-33. doi: 10.1128/IAI.67.6.2822-2833.1999.
Two new genes, mrpH and mrpJ, were identified downstream of mrpG in the mrp gene cluster encoding mannose-resistant Proteus-like (MR/P) fimbriae of uropathogenic Proteus mirabilis. Since the predicted MrpH has 30% amino acid sequence identity to PapG, the Galalpha(1-4)Gal-binding adhesin of Escherichia coli P fimbriae, we hypothesized that mrpH encodes the functional MR/P hemagglutinin. MR/P fimbriae, expressed in E. coli DH5alpha, conferred on bacteria both the ability to cause mannose-resistant hemagglutination and the ability to aggregate to form pellicles on the broth surface. Both a DeltamrpH mutant expressed in E. coli DH5alpha and an isogenic mrpH::aphA mutant of P. mirabilis were unable to produce normal MR/P fimbriae efficiently, suggesting that MrpH was involved in fimbrial assembly. Amino acid residue substitution of the N-terminal cysteine residues (C66S and C128S) of MrpH abolished the receptor-binding activity (hemagglutinating ability) of MrpH but allowed normal fimbrial assembly, supporting the notion that MrpH was the functional MR/P hemagglutinin. Immunogold electron microscopy of P. mirabilis HI4320 revealed that MrpH was located at the tip of MR/P fimbriae, also consistent with its role in receptor binding. The isogenic mrpH::aphA mutant of HI4320 was less able to colonize the urine, bladder, and kidneys in a mouse model of ascending urinary tract infection (P < 0.01), and therefore MR/P fimbriae contribute significantly to bacterial colonization in mice. While there are similarities between P. mirabilis MR/P and E. coli P fimbriae, there are more notable differences: (i) synthesis of the MrpH adhesin is required to initiate fimbrial assembly, (ii) MR/P fimbriae confer an aggregation phenotype, (iii) site-directed mutation of specific residues can abolish receptor binding but allows fimbrial assembly, and (iv) mutation of the adhesin gene abolishes virulence in a mouse model of ascending urinary tract infection.
在编码奇异变形杆菌（尿路致病性变形杆菌）的甘露糖抗性变形杆菌样（MR/P）菌毛的mrp基因簇中，在mrpG下游鉴定出两个新基因mrpH和mrpJ。由于预测的MrpH与大肠杆菌P菌毛的Galα(1-4)Gal结合粘附素PapG具有30%的氨基酸序列同一性，我们推测mrpH编码功能性MR/P血凝素。在大肠杆菌DH5α中表达的MR/P菌毛赋予细菌引起甘露糖抗性血凝的能力以及在肉汤表面聚集形成菌膜的能力。在大肠杆菌DH5α中表达的DeltamrpH突变体和奇异变形杆菌的同基因mrpH::aphA突变体均无法有效产生正常的MR/P菌毛，这表明MrpH参与菌毛组装。MrpH N端半胱氨酸残基（C66S和C128S）的氨基酸残基取代消除了MrpH的受体结合活性（血凝能力），但允许正常的菌毛组装，支持了MrpH是功能性MR/P血凝素的观点。奇异变形杆菌HI4320的免疫金电子显微镜显示，MrpH位于MR/P菌毛的尖端，这也与其在受体结合中的作用一致。HI4320的同基因mrpH::aphA突变体在小鼠上行性尿路感染模型中定殖于尿液、膀胱和肾脏的能力较弱（P < 0.01），因此MR/P菌毛对小鼠体内的细菌定殖有显著贡献。虽然奇异变形杆菌MR/P和大肠杆菌P菌毛之间存在相似性，但也有更显著的差异：（i）MrpH粘附素的合成是启动菌毛组装所必需的；（ii）MR/P菌毛赋予聚集表型；（iii）特定残基的定点突变可消除受体结合但允许菌毛组装；（iv）粘附素基因突变可消除小鼠上行性尿路感染模型中的毒力。
