Barthelme D, Scheele U, Dinkelaker S, Janoschka A, Macmillan F, Albers SV, Driessen AJM, Stagni MS, Bill E, Meyer-Klaucke W, Schünemann V, Tampé R. Structural Organization of Essential Iron-Sulfur Clusters in the Evolutionarily Highly Conserved ATP-binding Cassette Protein ABCE1.
J Biol Chem 2007;
282:14598-607. [PMID:
17355973 DOI:
10.1074/jbc.m700825200]
[Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ABC protein ABCE1, formerly named RNase L inhibitor RLI1, is one of the most conserved proteins in evolution and is expressed in all organisms except eubacteria. Because of its fundamental role in translation initiation and/or ribosome biosynthesis, ABCE1 is essential for life. Its molecular mechanism has, however, not been elucidated. In addition to two ABC ATPase domains, ABCE1 contains a unique N-terminal region with eight conserved cysteines, predicted to coordinate iron-sulfur clusters. Here we present detailed information on the type and on the structural organization of the Fe-S clusters in ABCE1. Based on biophysical, biochemical, and yeast genetic analyses, ABCE1 harbors two essential diamagnetic [4Fe-4S](2+) clusters with different electronic environments, one ferredoxin-like (CPX(n)CX(2)CX(2)C; Cys at positions 4-7) and one unique ABCE1-type cluster (CXPX(2)CX(3)CX(n)CP; Cys at positions 1, 2, 3, and 8). Strikingly, only seven of the eight conserved cysteines coordinating the Fe-S clusters are essential for cell viability. Mutagenesis of the cysteine at position 6 yielded a functional ABCE1 with the ferredoxin-like Fe-S cluster in a paramagnetic [3Fe-4S](+) state. Notably, a lethal mutation of the cysteine at position 4 can be rescued by ligand swapping with an adjacent, extra cysteine conserved among all eukaryotes.
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