A novel molecular chaperone-like protein found in yeast peroxisomes

该项目旨在了解非特异性脂质转移蛋白（nsLTP或SCP 2）的酵母同源物的生理作用，我们在热带假丝酵母的过氧化物酶体中发现了该蛋白，并将其命名为PXO-18。迄今为止，在过氧化物酶体中还没有发现分子伴侣或应激蛋白。我们的研究结果表明，PXP-18应该是一个可能的候选人。1）PXP-18被证明主要存在于基质的过氧化物酶体通过免疫电子显微镜，亚细胞分级，并通过输入的蛋白。PXP-18保护过氧化物酶体酰基辅酶A氧化酶（ACO）在48 ℃或70 ℃的热灭活。当在70 ℃加热15分钟，PXP-18和ACO亚基形成一个近化学计量的复合物，独立于它们的初始比例。游离ACO在30 ℃时从分离的复合物中自发释放。PXP-18在70 ℃时可逆地改变其二级结构，并以依赖于时间和温度的方式形成同源二聚体。二聚体PXP-18可以结合到部分变性的八聚体ACO以形成近化学计量复合物，防止它们进一步变性。2）线虫的cDNA克隆揭示了与硫解酶-SCP 2高度相似但缺少SCP 2部分的蛋白质（TLP）;硫解酶-SCP 2由来自哺乳动物SCP 2基因的较长mRNA编码，并显示3-氧代酰基-CoA硫解酶活性。TLP和PXP-18似乎代表了硫解酶-SCP 2的进化起源。PXP-18可以促进融合的硫解酶掺入到一个假定的β-氧化复合物，如泛素。泛素是一种应激蛋白，也以与核糖体蛋白融合的形式表达，并促进它们掺入核糖体。

This project aimed at understanding the physiological role of a yeast homologue of nonspecific lipid-transfer protein (nsLTP or SCP2) , which we found in peroxisomes of the yeast Candida tropicalis and named PXO-18. No molecular chaperone or stress protein has been found in peroxisomes thus far. Our results suggest that PXP-18 should be a possible candidate for it.1) PXP-18 was shown to be present predominantly in the matrix of peroxisomes by means of immunoeLectron microscopy, subcellular fractionation, and by importing the protein. PXP-18 protected peroxisomal acyl-CoA oxidase (ACO) from thermal inactivation at 48ﾟC or 70ﾟC.When heated at 70ﾟC for 15 min, PXP-18 and ACO subunit formed a nearstoichiometric complex, independent of their initial ratio. Free ACO was released from the isolated complex spontaneously at 30ﾟC.PXP-18 changed its secondary structure reversibly at 70ﾟC,and formed homodimers in a manner dependent on time and temperature. The dimeric PXP-18 may bind to octameric ACOs denatured partially to form the nearstoichiometric complex, preventing their further denaturation.2) A cDNA clone of the nematode Caenorhabditis elegans revealed a protein (TLP) that is highly similar to thiolase-SCP2 but lacks SCP2 moiety ; thiolase-SCP2 is encoded by the longer mRNA from the mammalian SCP2 gene and shows 3-oxoacyl-CoA thiolase activity. TLP and PXP-18 seems to represent the evolutionary origins of thiolase-SCP2. PXP-18 may facilitate the incorporation of the fused thiolase into a putative beta-oxidation complex, as ubiquitin does. Ubiquitin, a stress protein, is also expressed as a fused form with ribosomal proteins and facilitates their incorporation into ribosomes.