Molecular Sciences Laboratory, National Institute of Immunology, New Delhi 110067, India.
IUBMB Life. 2012 Jan;64(1):99-107. doi: 10.1002/iub.583.
The apicoplast of Plasmodium harbors several metabolic pathways. The enzymes required to perform these reactions are all nuclearly encoded and apicoplast targeted (NEAT) proteins. Plasmodium falciparum Enoyl-ACP Reductase (PfENR) is one such NEAT protein. The NEAT proteins have a transit peptide which is required for crossing the membranes of apicoplast. We studied the importance of basic residues like Arginine and Lysine within the transit peptide. Previous studies have suggested that all basic residues are essential for apicoplast trafficking. In this study, we demonstrate that only some of these residues are essential (K44, R48, K51, and R52), whereas others are dispensable (R40, K42, and K49). On mutating these specific residues, PfENR is not imported into the apicoplast and is mislocalized to the cytoplasm. We also demonstrate that these residues are also crucial for interaction with Hsp70-1, implying that interactions of Lysine 44, Arginine 48, Lysine 51, and Arginine 52 of the transit peptide with PfHsp70-1 are required for apicoplast trafficking. 15-Deoxyspergualin, which has earlier been proposed to interact with EEVD motif of PfHsp70-1 hinders the physical interaction between these cationic residues of PfENR and Hsp70-1. Hence, we propose that in the transport competent state of NEAT proteins some specific positively charged amino acids in the transit peptide interact with PfHsp70-1, and this interaction is essential for apicoplast targeting.
疟原虫的质体含有几种代谢途径。执行这些反应所需的酶都是核编码和质体靶向（NEAT）蛋白。恶性疟原虫烯酰基-ACP 还原酶（PfENR）就是这样一种 NEAT 蛋白。NEAT 蛋白具有跨膜所需的转运肽。我们研究了转运肽中碱性残基（如精氨酸和赖氨酸）的重要性。先前的研究表明，所有碱性残基对质体运输都是必不可少的。在这项研究中，我们证明只有一些碱性残基（K44、R48、K51 和 R52）是必需的，而其他残基是可有可无的（R40、K42 和 K49）。当突变这些特定的残基时，PfENR 不会被导入质体，而是错误定位到细胞质中。我们还证明，这些残基对于与 Hsp70-1 的相互作用也是至关重要的，这意味着转运肽中的赖氨酸 44、精氨酸 48、赖氨酸 51 和精氨酸 52 与 PfHsp70-1 的相互作用对于质体运输也是至关重要的。15-脱氧精胍菌素（15-Deoxyspergualin）早些时候被提议与 PfHsp70-1 的 EEVD 基序相互作用，它阻碍了 PfENR 的这些阳离子残基与 Hsp70-1 之间的物理相互作用。因此，我们提出，在 NEAT 蛋白的转运能力状态下，转运肽中的一些特定的正电荷氨基酸与 PfHsp70-1 相互作用，这种相互作用对于质体靶向是必不可少的。
