Rosenthal B, Mai Z, Caplivski D, Ghosh S, de la Vega H, Graf T, Samuelson J
Department of Tropical Public Health, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
J Bacteriol. 1997 Jun;179(11):3736-45. doi: 10.1128/jb.179.11.3736-3745.1997.
Entamoeba histolytica is an amitochondriate protozoan parasite with numerous bacterium-like fermentation enzymes including the pyruvate:ferredoxin oxidoreductase (POR), ferredoxin (FD), and alcohol dehydrogenase E (ADHE). The goal of this study was to determine whether the genes encoding these cytosolic E. histolytica fermentation enzymes might derive from a bacterium by horizontal transfer, as has previously been suggested for E. histolytica genes encoding heat shock protein 60, nicotinamide nucleotide transhydrogenase, and superoxide dismutase. In this study, the E. histolytica por gene and the adhE gene of a second amitochondriate protozoan parasite, Giardia lamblia, were sequenced, and their phylogenetic positions were estimated in relation to POR, ADHE, and FD cloned from eukaryotic and eubacterial organisms. The E. histolytica por gene encodes a 1,620-amino-acid peptide that contained conserved iron-sulfur- and thiamine pyrophosphate-binding sites. The predicted E. histolytica POR showed fewer positional identities to the POR of G. lamblia (34%) than to the POR of the enterobacterium Klebsiella pneumoniae (49%), the cyanobacterium Anabaena sp. (44%), and the protozoan Trichomonas vaginalis (46%), which targets its POR to anaerobic organelles called hydrogenosomes. Maximum-likelihood, neighbor-joining, and parsimony analyses also suggested as less likely E. histolytica POR sharing more recent common ancestry with G. lamblia POR than with POR of bacteria and the T. vaginalis hydrogenosome. The G. lamblia adhE encodes an 888-amino-acid fusion peptide with an aldehyde dehydrogenase at its amino half and an iron-dependent (class 3) ADH at its carboxy half. The predicted G. lamblia ADHE showed extensive positional identities to ADHE of Escherichia coli (49%), Clostridium acetobutylicum (44%), and E. histolytica (43%) and lesser identities to the class 3 ADH of eubacteria and yeast (19 to 36%). Phylogenetic analyses inferred a closer relationship of the E. histolytica ADHE to bacterial ADHE than to the G. lamblia ADHE. The 6-kDa FD of E. histolytica and G. lamblia were most similar to those of the archaebacterium Methanosarcina barkeri and the delta-purple bacterium Desulfovibrio desulfuricans, respectively, while the 12-kDa FD of the T. vaginalis hydrogenosome was most similar to the 12-kDa FD of gamma-purple bacterium Pseudomonas putida. E. histolytica genes (and probably G. lamblia genes) encoding fermentation enzymes therefore likely derive from bacteria by horizontal transfer, although it is not clear from which bacteria these amebic genes derive. These are the first nonorganellar fermentation enzymes of eukaryotes implicated to have derived from bacteria.
溶组织内阿米巴是一种无线粒体的原生动物寄生虫,具有多种类似细菌的发酵酶,包括丙酮酸:铁氧化还原蛋白氧化还原酶(POR)、铁氧化还原蛋白(FD)和乙醇脱氢酶E(ADHE)。本研究的目的是确定编码这些溶组织内阿米巴胞质发酵酶的基因是否可能通过水平转移来自细菌,正如之前有人提出的溶组织内阿米巴编码热休克蛋白60、烟酰胺核苷酸转氢酶和超氧化物歧化酶的基因那样。在本研究中,对另一种无线粒体的原生动物寄生虫蓝氏贾第鞭毛虫的溶组织内阿米巴por基因和adhE基因进行了测序,并根据从真核生物和细菌生物克隆的POR、ADHE和FD估计了它们的系统发育位置。溶组织内阿米巴por基因编码一个1620个氨基酸的肽,该肽包含保守的铁硫和硫胺焦磷酸结合位点。预测的溶组织内阿米巴POR与蓝氏贾第鞭毛虫的POR(34%)相比,与肺炎克雷伯氏菌(49%)、鱼腥藻属蓝细菌(44%)和阴道毛滴虫(46%)的POR的位置同一性更少,阴道毛滴虫将其POR靶向称为氢化酶体的厌氧细胞器。最大似然法、邻接法和简约法分析也表明,溶组织内阿米巴POR与蓝氏贾第鞭毛虫POR共享更近共同祖先的可能性小于与细菌和阴道毛滴虫氢化酶体的POR。蓝氏贾第鞭毛虫adhE编码一个888个氨基酸的融合肽,其氨基端为醛脱氢酶,羧基端为铁依赖性(3类)ADH。预测的蓝氏贾第鞭毛虫ADHE与大肠杆菌(49%)、丙酮丁醇梭菌(44%)和溶组织内阿米巴(43%)的ADHE具有广泛的位置同一性,与细菌和酵母的3类ADH的同一性较低(19%至36%)。系统发育分析推断,溶组织内阿米巴ADHE与细菌ADHE的关系比与蓝氏贾第鞭毛虫ADHE的关系更密切。溶组织内阿米巴和蓝氏贾第鞭毛虫的6 kDa FD分别与巴氏甲烷八叠球菌和脱硫脱硫弧菌的最相似,而阴道毛滴虫氢化酶体的12 kDa FD与恶臭假单胞菌的12 kDa FD最相似。因此,编码溶组织内阿米巴(可能还有蓝氏贾第鞭毛虫)发酵酶的基因可能通过水平转移来自细菌,尽管尚不清楚这些阿米巴基因来自哪些细菌。这些是首次被认为来自细菌的真核生物非细胞器发酵酶。