Becker P S, Akins D R, Radolf J D, Norgard M V
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235.
Infect Immun. 1994 Apr;62(4):1381-91. doi: 10.1128/iai.62.4.1381-1391.1994.
The recent discovery that abundant and immunogenic lipoproteins constitute the integral membrane proteins of Treponema pallidum has prompted efforts to investigate their importance in the physiology and ultrastructure of the organism and in immune responses during infection. Earlier studies identified a 38-kDa lipoprotein of T. pallidum believed to be specific to the pathogen. In the present study, monoclonal antibodies generated against the 38-kDa lipoprotein of T. pallidum reacted with cognate 37-kDa molecules in the nonpathogens Treponema phagedenis, Treponema denticola, and Treponema refringens. Cloning and expression of the 38-kDa-lipoprotein gene of T. pallidum in Escherichia coli revealed that the recombinant product displayed a slightly larger (39-kDa) apparent molecular mass but remained reactive with anti-38-kDa-protein monoclonal antibodies. The recombinant product was processed and acylated in E. coli. DNA and amino acid sequence analyses indicated an open reading frame encoding 403 amino acids, with the first 25 amino acids corresponding to a leader peptide terminated by a signal peptidase II processing site of Val-Val-Gly-Cys. The predicted mature protein is 378 amino acids in length with a deduced molecular weight of 40,422 (excluding acylation). Southern blotting failed to demonstrate in nonpathogenic treponemes genomic sequences homologous with the 38-kDa-lipoprotein gene of T. pallidum. Computer analysis revealed that the 38-kDa lipoprotein of T. pallidum had 34.2% identity and 58.9% similarity with the glucose/galactose-binding protein (MglB) of E. coli and Salmonella typhimurium. Furthermore, of the 19 amino acids of MglB involved in carbohydrate binding, the 38-kDa lipoprotein had identity with 11. These studies have allowed the first putative functional assignment (carbohydrate binding) to a T. pallidum integral membrane protein. Recognition of this potential physiological role for the 38-kDa lipoprotein underscores the possibility that the membrane biology of T. pallidum may more closely resemble that of gram-positive organisms, which also utilize lipoproteins as anchored transporters, than that of gram-negative bacteria to which T. pallidum often is analogized.
最近发现，大量且具有免疫原性的脂蛋白构成了梅毒螺旋体的整合膜蛋白，这促使人们努力研究它们在该生物体的生理学、超微结构以及感染期间免疫反应中的重要性。早期研究鉴定出一种梅毒螺旋体的38 kDa脂蛋白，认为它是该病原体特有的。在本研究中，针对梅毒螺旋体38 kDa脂蛋白产生的单克隆抗体与非致病性密螺旋体噬齿密螺旋体、齿垢密螺旋体和屈折密螺旋体中的同源37 kDa分子发生反应。梅毒螺旋体38 kDa脂蛋白基因在大肠杆菌中的克隆和表达表明，重组产物显示出稍大（39 kDa）的表观分子量，但仍与抗38 kDa蛋白单克隆抗体发生反应。重组产物在大肠杆菌中进行了加工和酰化。DNA和氨基酸序列分析表明有一个编码403个氨基酸的开放阅读框，前25个氨基酸对应于一个由Val-Val-Gly-Cys的信号肽酶II加工位点终止的前导肽。预测的成熟蛋白长度为378个氨基酸，推导分子量为40,422（不包括酰化）。Southern印迹未能在非致病性密螺旋体中证明与梅毒螺旋体38 kDa脂蛋白基因同源的基因组序列。计算机分析表明，梅毒螺旋体的38 kDa脂蛋白与大肠杆菌和鼠伤寒沙门氏菌的葡萄糖/半乳糖结合蛋白（MglB）有34.2%的同一性和58.9%的相似性。此外，在MglB中参与碳水化合物结合的19个氨基酸中，38 kDa脂蛋白与其中11个氨基酸相同。这些研究首次对梅毒螺旋体整合膜蛋白进行了假定的功能分配（碳水化合物结合）。认识到38 kDa脂蛋白的这种潜在生理作用强调了这样一种可能性，即梅毒螺旋体的膜生物学可能更类似于革兰氏阳性菌（它们也利用脂蛋白作为锚定转运蛋白），而不是通常与之相类比的革兰氏阴性菌。
