Guyard Cyril, Battisti James M, Raffel Sandra J, Schrumpf Merry E, Whitney Adeline R, Krum Jonathan G, Porcella Stephen F, Rosa Patricia A, DeLeo Frank R, Schwan Tom G
Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840, USA.
Mol Microbiol. 2006 May;60(3):710-22. doi: 10.1111/j.1365-2958.2006.05122.x.
The spirochaetes that cause tick-borne relapsing fever and Lyme disease are closely related human pathogens, yet they differ significantly in their ecology and pathogenicity. Genome sequencing of two species of relapsing fever spirochaetes, Borrelia hermsii and Borrelia turicatae, identified a chromosomal open reading frame, designated bhpA, not present in the Lyme disease spirochaete Borrelia burgdorferi. The predicted amino acid sequence of bhpA was homologous with the HtrA serine proteases, which are involved with stress responses and virulence in other bacteria. B. hermsii produced an active serine protease that was recognized by BhpA antibodies and the recombinant BhpA protein-degraded beta-casein. bhpA was transcribed in vitro at all growth temperatures and transcription levels were slightly elevated at higher temperatures. These results correlated with the synthesis of BhpA during B. hermsii infection in mice. With the exception of Borrelia recurrentis, the bhpA gene, protein and enzymatic activity were found in all relapsing fever spirochaetes, but not in Lyme disease or related spirochaetes. Heterologous expression of bhpA in B. burgdorferi increased the spirochaete's resistance to both oxidative stress and killing by human neutrophils. Therefore, we propose that bhpA encodes a unique and functional serine protease in relapsing fever spirochaetes. This periplasmic enzyme may prevent the accumulation of proteins damaged by the innate immune response and contribute to the ability of the relapsing fever spirochaetes to achieve high cell densities in blood.
引起蜱传回归热和莱姆病的螺旋体是密切相关的人类病原体，但它们在生态学和致病性方面存在显著差异。对两种回归热螺旋体——赫氏疏螺旋体（Borrelia hermsii）和杜氏疏螺旋体（Borrelia turicatae）进行基因组测序时，发现了一个染色体开放阅读框，命名为bhpA，而在莱姆病螺旋体伯氏疏螺旋体（Borrelia burgdorferi）中不存在该基因。bhpA预测的氨基酸序列与HtrA丝氨酸蛋白酶同源，HtrA丝氨酸蛋白酶在其他细菌的应激反应和毒力方面发挥作用。赫氏疏螺旋体产生一种活性丝氨酸蛋白酶，该酶能被BhpA抗体识别，且重组BhpA蛋白可降解β-酪蛋白。bhpA在所有生长温度下均可在体外转录，且在较高温度下转录水平略有升高。这些结果与赫氏疏螺旋体感染小鼠期间BhpA的合成情况相关。除回归热疏螺旋体（Borrelia recurrentis）外，在所有回归热螺旋体中均发现了bhpA基因、蛋白和酶活性，但在莱姆病螺旋体或相关螺旋体中未发现。在伯氏疏螺旋体中异源表达bhpA可增强螺旋体对氧化应激的抵抗力以及对人中性粒细胞杀伤作用的抵抗力。因此，我们认为bhpA在回归热螺旋体中编码一种独特且具有功能的丝氨酸蛋白酶。这种周质酶可能会阻止因固有免疫反应而受损的蛋白质积累，并有助于回归热螺旋体在血液中达到高细胞密度。
