1p3w
From Proteopedia
X-ray crystal structure of E. coli IscS
Structural highlights
Function[ISCS_ECOLI] Master enzyme that delivers sulfur to a number of partners involved in Fe-S cluster assembly, tRNA modification or cofactor biosynthesis. Catalyzes the removal of elemental sulfur from cysteine to produce alanine. Functions as a sulfur delivery protein for Fe-S cluster synthesis onto IscU, an Fe-S scaffold assembly protein, as well as other S acceptor proteins. Preferentially binds to disordered IscU on which the Fe-S is assembled, IscU converts to the structured state and then dissociates from IscS to transfer the Fe-S to an acceptor protein. Also functions as a selenium delivery protein in the pathway for the biosynthesis of selenophosphate. Transfers sulfur onto 'Cys-456' of ThiI and onto 'Cys-19' of TusA in transpersulfidation reactions.[1] [2] [3] [4] [5] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedIscS is a widely distributed cysteine desulfurase that catalyzes the pyridoxal phosphate-dependent desulfuration of L-cysteine and plays a central role in the delivery of sulfur to a variety of metabolic pathways. We report the crystal structure of Escherichia coli IscS to a resolution of 2.1A. The crystals belong to the space group P2(1)2(1)2(1) and have unit cell dimensions a=73.70A, b=101.97A, c=108.62A (alpha=beta=gamma=90 degrees ). Molecular replacement with the Thermotoga maritima NifS model was used to determine phasing, and the IscS model was refined to an R=20.6% (R(free)=23.6%) with two molecules per asymmetric unit. The structure of E.coli IscS is similar to that of T.maritima NifS with nearly identical secondary structure and an overall backbone r.m.s. difference of 1.4A. However, in contrast to NifS a peptide segment containing the catalytic cysteine residue (Cys328) is partially ordered in the IscS structure. This segment of IscS (residues 323-335) forms a surface loop directed away from the active site pocket. Cys328 is positioned greater than 17A from the pyridoxal phosphate cofactor, suggesting that a large conformational change must occur during catalysis in order for Cys328 to participate in nucleophilic attack of a pyridoxal phosphate-bound cysteine substrate. Modeling suggests that rotation of this loop may allow movement of Cys328 to within approximately 3A of the pyridoxal phosphate cofactor. Crystal structure of IscS, a cysteine desulfurase from Escherichia coli.,Cupp-Vickery JR, Urbina H, Vickery LE J Mol Biol. 2003 Jul 25;330(5):1049-59. PMID:12860127[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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