A novel potential surface protein in Trichomonas vaginalis contains a leucine-rich repeat shared by micro-organisms from all three domains of life
A novel potential surface protein in Trichomonas vaginalis contains a leucine-rich repeat shared by micro-organisms from all three domains of life
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DOI：
10.1016/s0166-6851(02)00211-6
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发表时间：
2002-11-01
影响因子：
1.5
通讯作者：
Embley, TM
中科院分区：
文献类型：
--
作者：
Hirt, RP;Harriman, N;Embley, TM
每年约有2亿人感染阴道毛滴虫，使其成为数量最多的非病毒性性传播疾病[1,2]。滴虫感染除了会引起严重的阴道炎症外，还与子宫颈癌、易感染艾滋病毒、不孕症以及产前和产后并发症有关。阴道绦虫的长期感染需要这种寄生虫能够在阴道内定居并持续存在。与阴道上皮细胞（VEC）、红细胞和淋巴细胞的相互作用都被认为在这一过程中发挥重要作用[1,3]。一旦阴道上皮因细胞致病性和月经周期脱落，阴道梭菌也可以结合宿主细胞外基质（ECM）蛋白，如纤维连接蛋白（Fn）和层粘连蛋白[4]，以及血浆蛋白，如纤维蛋白原[5]。已有实验证据表明，阴道T.与VEC和ECM蛋白之间的结合是通过特定的proteinÁ/蛋白相互作用进行的[4,6]。然而，参与这些相互作用的阴道绦虫表面蛋白尚未被确定。我们现在已经确定了一个编码候选表面蛋白的基因，根据其序列特征，我们假设该基因可能在这一过程中发挥作用。我们从T. vaginalis G3 cDNA文库中鉴定出两个克隆，它们编码一种假定的蛋白，在BLAST搜索中[8]与真菌性牙周病原体Bacteroides forsythus[9]的BspA蛋白具有显著的局部序列相似性。1）. BspA是一种细胞表面蛋白，结合ECM成分Fn和凝血因子纤维蛋白原，也是一种主要的免疫原[9]。因此，BspA被认为在连翘B. forsythus bbb .口腔定植中起重要作用。我们分离出相应的毛滴虫基因组克隆（文库由John Logsdon Jr.和Andrew Roger， Halifax， Canada提供），编码一个假定的625个氨基酸的蛋白，我们将其命名为TvBspA-like-625（图1a）。正如之前报道的阴道绦虫基因一样，非蛋白质编码的5？和3 ?侧翼区域在ORF上富含A′/T[10,11]。还有两个可能的转录启动序列，接近假定的起始密码子，类似于已知的共识序列[10]（见GenBank条目AY101349的DNA序列）。连翘BspA蛋白结构域与宿主蛋白结合的一个关键特征是一个富含亮氨酸的重复序列（LRR）。该LRR是BspA与编码蛋白TvBspA-like-625的翻译开放阅读框之间序列相似性较强的区域（图1a）。tvbpa -like-625的n端串联含有12个LRR（每个23Á/25个残基），加上两个相邻的保守性较差的LRR（图1a和B）。还有一个富含脯氨酸的重复序列（PRR）和富含天冬酰胺的重复序列（12个串联排列的重复序列，每个重复序列包含两个缩写：ECM，细胞外基质；HGT，水平基因转移；LRR，富含亮氨酸的重复序列；PRR，富含脯氨酸的重复序列；TpLRR，密螺旋体型富含亮氨酸的重复序列；TM，跨膜结构域）。注：本文报告的核苷酸序列数据可在GenBankTM数据库中获得（登录号：AY101349）。
Approximately 200 million people are infected by Trichomonas vaginalis annually making it the most abundant, non-viral, sexually transmitted disease [1, 2]. As well as causing severe vaginal inflammation, infection with Trichomonas is linked to cervical cancer, predisposition to HIV infection, infertility and preand post-natal complications [2]. Long-term infection by T. vaginalis requires that the parasite is able to colonise and persist within the vagina. Interactions with vaginal epithelial cells (VEC), erythrocytes and lymphocytes are all thought to play important roles in this process [1, 3]. Once the vaginal epithelium has been exfoliated, by cytopathogenicity and during the menstrual cycle, T. vaginalis can also bind to host extracellular matrix (ECM) proteins, such as fibronectin (Fn) and laminin [4], and to plasma proteins such as fibrinogen [5]. There is already experimental evidence suggesting that the binding between T. vaginalis and VEC and ECM proteins take place through specific proteinÁ/protein interactions [4, 6]. However, the T. vaginalis surface proteins that are involved in these interactions have not been identified [7]. We have now identified a gene encoding a candidate surface protein which, based upon its sequence features, we hypothesise may play a role in this process. We identified two clones from a T. vaginalis G3 cDNA library encoding a putative protein with significant localised sequence similarity in BLAST searches [8] to the BspA protein from the eubacterial periodontal pathogen Bacteroides forsythus [9](Fig. 1). BspA is a cell surface protein which binds Fn, a component of the ECM, as well as the clotting factor fibrinogen, and it is also a major immunogen [9]. BspA is thus thought to play an important role in the colonization of the oral cavity by B. forsythus [9]. We isolated a corresponding Trichomonas genomic clone (library provided by John Logsdon Jr. and Andrew Roger, Halifax, Canada) coding for a putative protein of 625 amino acids that we named TvBspA-like-625 (Fig. 1 A). As previously reported for T. vaginalis genes, the non-protein coding 5? and 3? flanking regions are enriched in A'/T over the ORF [10, 11]. There are also two possible transcription initiator sequences, close to the putative starting codon, that resemble known consensus sequences [10](see GenBank entry AY101349 for DNA sequence). A key feature of the B. forsythus BspA protein domain, involved in binding to host proteins, is a leucine-rich repeat (LRR). This LRR is the region of strong sequence similarity between BspA and the translated open reading frame coding for the protein TvBspA-like-625 (Fig. 1 A). The N-terminus of TvBspA-like-625 contains 12 LRR (each of 23Á/25 residues) in tandem, plus two adjacent less well-conserved LRR (Fig. 1 A and B). There is also a proline-rich repeat (PRR) and asparagine-rich repeat (12 tandemly arranged repeats of 7 amino acids each containing two PAbbreviations: ECM, extracellular matrix; HGT, horizontal gene transfer; LRR, leucine-rich repeat; PRR, proline-rich repeat; TpLRR, Treponema type leucine-rich repeat; TM, transmembrane domain. Note: Nucleotide sequence data reported in this paper are available in the GenBankTM data base (accession number: AY101349).