Lysosomal acid lipase (LAL) plays an important role in lipid metabolism by performing hydrolysis of triglycerides and cholesteryl esters in the lysosome. Based upon characteristics of LAL purified from human liver, it has been proposed that LAL is a proprotein with a 55 residue propeptide that may be essential for proper folding, intracellular transport, or enzymatic function. However, the biological significance of such a propeptide has not been fully elucidated. In this study, we have performed a series of studies in cultured HepG2 and HeLa cells to determine the role of the putative propeptide. However, by Western blot analysis and subcellular fractionation, we have not been able to identify a cleaved LAL lacking the N-terminal 55 residues. Moreover, mutating residues surrounding the putative cleavage site at Lys76 ↓ in order to disrupt a proteinase recognition sequence, did not affect LAL activity. Furthermore, forcing cleavage at Lys76 ↓ by introducing the optimal furin cleavage site RRRR↓EL between residues 76 and 77, did not affect LAL activity. These data, in addition to bioinformatics analyses, indicate that LAL is not a proprotein. Thus, it is possible that the previously reported cleavage at Lys76 ↓ could have resulted from exposure to proteolytic enzymes during the multistep purification procedure.

中文翻译：

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溶酶体酸性脂肪酶没有前肽，不应被认为是前蛋白。

溶酶体酸性脂肪酶（LAL）通过在溶酶体中进行甘油三酸酯和胆固醇酯的水解，在脂质代谢中起重要作用。基于从人肝脏中纯化的LAL的特性，有人提出LAL是具有55个残基前肽的原蛋白，这对于适当的折叠，细胞内运输或酶功能可能是必不可少的。但是，尚未充分阐明这种前肽的生物学意义。在这项研究中，我们对培养的HepG2和HeLa细胞进行了一系列研究，以确定推定的前肽的作用。但是，通过蛋白质印迹分析和亚细胞分级分离，我们未能鉴定出缺少N末端55个残基的裂解LAL。而且，为了破坏蛋白酶识别序列，在Lys76↓的假定切割位点周围突变的残基不影响LAL活性。此外，通过在残基76和77之间引入最佳弗林蛋白酶切割位点RRRR↓EL来迫使在Lys76↓的切割不影响LAL活性。这些数据，除了生物信息学分析之外，还表明LAL不是一种前蛋白。因此，有可能先前报道的Lys76↓的切割可能是由于在多步纯化过程中暴露于蛋白水解酶而导致的。表明LAL不是一种前蛋白。因此，有可能先前报道的Lys76↓的切割可能是由于在多步纯化过程中暴露于蛋白水解酶而导致的。表明LAL不是一种前蛋白。因此，有可能先前报道的Lys76↓的切割可能是由于在多步纯化过程中暴露于蛋白水解酶而导致的。