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J. Biol. Chem., Vol. 283, Issue 12, 7962-7971, March 21, 2008

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X-ray Structure of the Complete ABC Enzyme ABCE1 from Pyrococcus abyssi^*

From the Center for Integrated Protein Science and Center for Advanced Photonics at the Gene Center, Ludwig-Maximilians-University Munich, D-81377 Munich, Germany

The ATP binding cassette enzyme ABCE1 (also known as RNase-L (ribonuclease L) inhibitor, Pixie, and HP68), one of the evolutionary most sequence-conserved enzymes, functions in translation initiation, ribosome biogenesis, and human immunodeficiency virus capsid assembly. However, its structural mechanism and biochemical role in these processes have not been revealed. We determined the crystal structure of Pyrococcus abyssi ABCE1 in complex with Mg²⁺ and ADP to 2.8Å resolution. ABCE1 consists of four structural domains. Two nucleotide binding domains are arranged in a head-to-tail orientation by a hinge domain, suggesting that these domains undergo the characteristic tweezers-like powerstroke of ABC enzymes. In contrast to all other known ABC enzymes, ABCE1 has a N-terminal iron-sulfur-cluster (FeS) domain. The FeS domain contains two [4Fe-4S] clusters and is structurally highly related to bacterial-type ferredoxins. However, one cluster is coordinated by an unusual CX₄CX_3/4C triad. Surprisingly, intimate interactions of the FeS domain with the adenine and ribose binding Y-loop on nucleotide binding domain 1 suggest a linkage between FeS domain function and ATP-induced conformational control of the ABC tandem cassette. The structure substantially expands the functional architecture of ABC enzymes and raises the possibility that ABCE1 is a chemomechanical engine linked to a redox process.

Received for publication, August 31, 2007 , and in revised form, December 6, 2007.

The atomic coordinates and structure factors (code 3BK7) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* This work was supported by Deutsche Forschungsgemeinschaft Grants HO2489/2 and SFB455 (to K. P. H.). 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. 1.

¹ To whom correspondence should be addressed: Feodor-Lynen-Strasse 25, D-81377 Munich, Germany. Tel.: 49-89-2180-76953; Fax: 49-89-2180-76999; E-mail: hopfner{at}lmb.uni-muenchen.de.

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