Research Unit for Tropical Diseases, de Duve Institute and Laboratory of Biochemistry, Université catholique de Louvain, TROP 74.39, Avenue Hippocrate 74, B-1200 Brussels, Belgium.
Int J Parasitol. 2011 Oct;41(12):1273-83. doi: 10.1016/j.ijpara.2011.07.009. Epub 2011 Aug 26.
Thiolases are enzymes that remove an acetyl-coenzyme A group from acyl-CoA in the catabolic β-oxidation of fatty acids, or catalyse the reverse condensation reaction for anabolic processes such as the biosynthesis of sterols and ketone bodies. In humans, six homologous isoforms of thiolase have been described, differing from each other in sequence, oligomeric state, substrate specificity and subcellular localization. A bioinformatics analysis of parasite genomes, being (i) different species of African trypanosomes, (ii) Trypanosoma cruzi and (iii) Leishmania spp., using the six human sequences as queries, showed that the distribution of thiolases in human and each of the studied Trypanosomatidae is completely different. Only one of these isoforms, called SCP2-thiolase, was found in each of the Trypanosomatidae, whereas the TFE-thiolase was also found in T. cruzi and Leishmania spp., and the AB-thiolase only in T. cruzi. Each of the trypanosomatid thiolases clusters with its orthologues from other organisms in a phylogenetic analysis and shares with them the isoform-specific sequence fingerprints. The single T. brucei SCP2-thiolase has been expressed in Escherichia coli and characterized. It shows activity in both the degradative and synthetic directions. Transcripts of this thiolase were detected in both bloodstream- and procyclic-form trypanosomes, but the protein was found only in the procyclic form. The encoded protein has both a predicted N-terminal mitochondrial signal peptide and a C-terminal candidate type 1 peroxisomal-targeting signal for sorting it into glycosomes. However experimentally, only a mitochondrial localization was found for both procyclic trypanosomes grown with glucose and cells cultured with amino acids as an energy source. When the thiolase expression in procyclic cells was knocked down by RNA interference, no important change in growth rate occurred, irrespective of whether the cells were grown with or without glucose, indicating that the metabolic pathway(s) involving this enzyme is/are not essential for the parasite under either of these growth conditions.
硫解酶是一种酶，可在脂肪酸的分解β-氧化中从酰基辅酶 A 去除乙酰辅酶 A 基团，或者催化用于合成固醇和酮体等合成过程的逆缩合反应。在人类中，已经描述了六种同源的硫解酶同工型，它们在序列、寡聚状态、底物特异性和亚细胞定位方面彼此不同。使用六个人类序列作为查询，对寄生虫基因组进行生物信息学分析，分析了（i）不同种的非洲锥虫、（ii）克氏锥虫和（iii）利什曼原虫，结果表明硫解酶在人类和研究的每一种锥虫中的分布完全不同。在每一种锥虫中仅发现了这些同工型中的一种，称为 SCP2-硫解酶，而 TFE-硫解酶也在克氏锥虫和利什曼原虫中发现，而 AB-硫解酶仅在克氏锥虫中发现。在系统发育分析中，每一种锥虫硫解酶都与其他生物的同源物聚类，并与它们共享同工型特异性序列指纹。单个 T. brucei SCP2-硫解酶已在大肠杆菌中表达并进行了表征。它在降解和合成两个方向都显示出活性。在血液期和前鞭毛体期的锥虫中均检测到这种硫解酶的转录本，但仅在前鞭毛体期发现该蛋白。该编码蛋白既有预测的 N 端线粒体信号肽，又有 C 端候选 1 型过氧化物酶体靶向信号，用于将其分拣到糖酵体中。然而，实验仅发现葡萄糖生长的前鞭毛体和以氨基酸为能源的细胞培养物中，该蛋白具有线粒体定位。当 RNA 干扰敲低前鞭毛体细胞中的硫解酶表达时，无论细胞是否在有或没有葡萄糖的情况下生长，其生长速度都没有重要变化，这表明该酶涉及的代谢途径在这两种生长条件下对寄生虫都不是必需的。
