Sundararaj Srinivasan, Saxena Ajay K, Sharma Ruby, Vashisht Kapil, Sharma Supriya, Anvikar Anup, Dixit Rajnikant, Rosenthal Philip J, Pandey Kailash C
Host-Parasite Interaction Biology Group, National Institute of Malaria Research, Indian Council of Medical Research, Dwarka, New Delhi, India.
Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
PLoS One. 2014 Apr 3;9(4):e93008. doi: 10.1371/journal.pone.0093008. eCollection 2014.
Cysteine proteases play a crucial role in the development of the human malaria parasites Plasmodium falciparum and Plasmodium vivax. Our earlier studies demonstrated that these enzymes are equipped with specific domains for defined functions and further suggested the mechanism of activation of cysteine proteases. The activities of these proteases are regulated by a new class of endogenous inhibitors of cysteine proteases (ICPs). Structural studies of the ICPs of Trypanosoma cruzi (chagasin) and Plasmodium berghei (PbICP) indicated that three loops (termed BC, DE, and FG) are crucial for binding to target proteases. Falstatin, an ICP of P. falciparum, appears to play a crucial role in invasion of erythrocytes and hepatocytes. However, the mechanism of inhibition of cysteine proteases by falstatin has not been established. Our study suggests that falstatin is the first known ICP to function as a multimeric protein. Using site-directed mutagenesis, hemoglobin hydrolysis assays and peptide inhibition studies, we demonstrate that the BC loop, but not the DE or FG loops, inhibits cysteine proteases of P. falciparum and P. vivax via hydrogen bonds. These results suggest that the BC loop of falstatin acts as a hot-spot target for inhibiting malarial cysteine proteases. This finding suggests new strategies for the development of anti-malarial agents based on protease-inhibitor interactions.
半胱氨酸蛋白酶在人类疟原虫恶性疟原虫和间日疟原虫的发育过程中起着至关重要的作用。我们早期的研究表明，这些酶具有特定的功能结构域，并进一步揭示了半胱氨酸蛋白酶的激活机制。这些蛋白酶的活性受一类新型的半胱氨酸蛋白酶内源性抑制剂（ICPs）调控。对克氏锥虫（查加辛）和伯氏疟原虫（PbICP）的ICPs的结构研究表明，三个环（称为BC、DE和FG）对于与靶蛋白酶的结合至关重要。恶性疟原虫的ICP法尔斯他汀似乎在红细胞和肝细胞的入侵中起关键作用。然而，法尔斯他汀对半胱氨酸蛋白酶的抑制机制尚未明确。我们的研究表明，法尔斯他汀是首个已知的作为多聚体蛋白发挥作用的ICP。通过定点诱变、血红蛋白水解试验和肽抑制研究，我们证明BC环而非DE或FG环通过氢键抑制恶性疟原虫和间日疟原虫的半胱氨酸蛋白酶。这些结果表明，法尔斯他汀的BC环是抑制疟原虫半胱氨酸蛋白酶的热点靶点。这一发现为基于蛋白酶-抑制剂相互作用开发抗疟药物提供了新策略。
