1t3i
From Proteopedia
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Structure of slr0077/SufS, the Essential Cysteine Desulfurase from Synechocystis PCC 6803
Overview
Cysteine desulfurases, designated NifS, IscS, and SufS, cleave L-cysteine, to form alanine and an enzyme cysteinyl persulfide intermediate. Genetic, studies on the photosynthetic cyanobacterium Synechocystis sp. PCC 6803, have shown that of the three Nif/Isc/SufS-like proteins encoded in its, genome only the sequence group II protein, Slr0077/SufS, is essential., This protein has been overexpressed in Escherichia coli, purified to, homogeneity, shown to bind pyridoxal-5'-phosphate (PLP) and to catalyze, cysteine desulfuration, and characterized in terms of its structure and, kinetics. The results suggest that catalysis in the absence of accessory, factors has two constituent pathways, one involving nucleophilic attack by, C372 to form the Slr0077/SufS-bound cysteinyl persulfide intermediate and, the second involving intermolecular attack by the sulfur of a second, molecule of the substrate on the initial l-cysteine-PLP complex to form, free l-cysteine persulfide. The second pathway is operant in the C372A, variant protein, explaining why it retains significant activity, which is, proportional to the concentration of l-cysteine (i.e., does not saturate)., C-S bond cleavage by the first (normal) pathway is considerably less, efficient than the equivalent step in a group I desulfurase (Slr0387) from, the same organism (characterized in the accompanying paper). The 1.8 A, crystal structure of the protein, which is very similar to that previously, reported for E. coli SufS, shows that the loop on which C372 resides is, well-ordered and shorter by 11 residues than the corresponding disordered, loop of the group I NifS-like protein from Thermotoga maritima. Sequence, comparisons establish that the T. maritima and Slr0387 proteins have loops, of similar length. The combined structural and kinetic data imply that the, modest activity of Slr0077/SufS and other SufS proteins in comparison to, their sequence group I (NifS/IscS-like) paralogues results from, inefficiency in the nucleophilic attack step associated with differences, in the structure or dynamics of this loop. The recent reports that SufS, proteins can be activated manyfold by binding to SufE thus implies that, the accessory protein either accelerates nucleophilic attack by the, conserved cysteine residue of SufS by a conformational mechanism or itself, contributes a nucleophilic cysteine for more efficient intermolecular, attack.
About this Structure
1T3I is a Single protein structure of sequence from Synechocystis sp. with 2OS, PLP and GOL as ligands. Active as Cysteine desulfurase, with EC number 2.8.1.7 Full crystallographic information is available from OCA.
Reference
Kinetic and structural characterization of Slr0077/SufS, the essential cysteine desulfurase from Synechocystis sp. PCC 6803., Tirupati B, Vey JL, Drennan CL, Bollinger JM Jr, Biochemistry. 2004 Sep 28;43(38):12210-9. PMID:15379559
Page seeded by OCA on Wed Nov 21 02:57:31 2007
