Ponpuak Marisa, Klemba Michael, Park Mehea, Gluzman Ilya Y, Lamppa Gayle K, Goldberg Daniel E
Howard Hughes Medical Institute, Washington University, Departments of Molecular Microbiology and Medicine, St. Louis, MO 63110, USA.
Mol Microbiol. 2007 Jan;63(2):314-34. doi: 10.1111/j.1365-2958.2006.05443.x. Epub 2006 Oct 27.
Falcilysin (FLN) is a zinc metalloprotease thought to degrade globin peptides in the acidic vacuole of the human malaria parasite Plasmodium falciparum. The enzyme has been found to have acidic or neutral pH optima on different peptides and to have additional distribution outside the food vacuole. These data suggested that FLN has an additional function in the parasite. To further probe the functions of FLN, we created a transgenic parasite clone expressing a chromosomally encoded FLN-GFP fusion. Unexpectedly, FLN was found in the apicoplast, an essential chloroplast-like organelle. Nuclear encoded apicoplast proteins are targeted to the organelle by a bipartite N-terminal sequence comprised of a signal sequence followed by a positively charged transit peptide domain. Free transit peptides are thought to be toxic to the plastid and need to be rapidly degraded after proteolytic release from proproteins. We hypothesized that FLN may participate in transit peptide degradation in the apicoplast based on its preference for basic residues at neutral pH and on phylogenetic comparison with other M16 family metalloproteases. In vitro cleavage by FLN of the transit peptide from the apicoplast-resident acyl carrier protein supports this idea. The importance of FLN for parasite development is suggested by our inability to truncate the chromosomal FLN open reading frame. Our work indicates that FLN is an attractive target for antimalarial development.
镰刀溶素（FLN）是一种锌金属蛋白酶，被认为可在人类疟原虫恶性疟原虫的酸性液泡中降解珠蛋白肽。已发现该酶对不同肽具有酸性或中性pH最适值，并且在食物泡外有额外分布。这些数据表明FLN在寄生虫中具有额外功能。为了进一步探究FLN的功能，我们创建了一个表达染色体编码的FLN-GFP融合蛋白的转基因寄生虫克隆。出乎意料的是，在顶质体（一种必需的类叶绿体细胞器）中发现了FLN。核编码的顶质体蛋白通过由信号序列后跟带正电荷的转运肽结构域组成的二分N端序列靶向该细胞器。游离的转运肽被认为对质体有毒，需要在从前体蛋白中蛋白水解释放后迅速降解。基于其在中性pH下对碱性残基的偏好以及与其他M16家族金属蛋白酶的系统发育比较，我们假设FLN可能参与顶质体中转运肽的降解。FLN对顶质体驻留的酰基载体蛋白的转运肽进行体外切割支持了这一观点。我们无法截短染色体FLN开放阅读框，这表明FLN对寄生虫发育很重要。我们的工作表明FLN是抗疟药物开发的一个有吸引力的靶点。
