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J. Biol. Chem., Vol. 281, Issue 28, 18914-18917, July 14, 2006

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The -Subunit of Leishmania F₁ ATP Synthase Hydrolyzes ATP in Presence of tRNA^*

From the Genetic Engineering Laboratory, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Calcutta 700032, India

Import of tRNAs into the mitochondria of the kinetoplastid protozoon Leishmania requires the tRNA-dependent hydrolysis of ATP leading to the generation of membrane potential through the pumping of protons. Subunit RIC1 of the inner membrane RNA import complex is a bi-functional protein that is identical to the -subunit of F₁F₀ ATP synthase and specifically binds to a subset (Type I) of importable tRNAs. We show that recombinant, purified RIC1 is a Type I tRNA-dependent ATP hydrolase. The activity was insensitive to oligomycin, sensitive to mutations within the import signal of the tRNA, and required the cooperative interaction between the ATP-binding and C-terminal domains of RIC1. The ATPase activity of the intact complex was inhibited by anti-RIC1 antibody, while knockdown of RIC1 in Leishmania tropica resulted in deficiency of the tRNA-dependent ATPase activity of the mitochondrial inner membrane. Moreover, RIC1 knockdown extracts failed to generate a membrane potential across reconstituted proteoliposomes, as shown by a rhodamine 123 uptake assay, but activity was restored by adding back purified RIC1. These observations identify RIC1 as a novel form of the F₁ ATP synthase -subunit that acts as the major energy transducer for tRNA import.

Received for publication, April 13, 2006 , and in revised form, May 22, 2006.

^* This work was supported in part by grants from the Department of Science and Technology and the Council of Scientific and Industrial Research (CSIR Project number SMM003). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by a fellowship from CSIR.

² To whom correspondence should be addressed. Tel.: 91-33-2473-3491 (ext. 136); Fax: 91-33-2473-5197; E-mail: sadhya{at}iicb.res.in.

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