1olt: Difference between revisions

'Radical SAM' enzymes generate catalytic radicals by combining a 4Fe-4S, cluster and S-adenosylmethionine (SAM) in close proximity. We present the, first crystal structure of a Radical SAM enzyme, that of HemN, the, Escherichia coli oxygen-independent coproporphyrinogen III oxidase, at, 2.07 A resolution. HemN catalyzes the essential conversion of, coproporphyrinogen III to protoporphyrinogen IX during heme biosynthesis., HemN binds a 4Fe-4S cluster through three cysteine residues conserved in, all Radical SAM enzymes. A juxtaposed SAM coordinates the fourth Fe ion, through its amide nitrogen and carboxylate oxygen. The SAM sulfonium, sulfur is near both the Fe (3.5 A) and a neighboring sulfur of the cluster, (3.6 A), allowing single electron transfer from the 4Fe-4S cluster to the, SAM sulfonium. SAM is cleaved yielding a highly oxidizing 5'-deoxyadenosyl, radical. HemN, strikingly, binds a second SAM immediately adjacent to the, first. It may thus successively catalyze two propionate decarboxylations., The structure of HemN reveals the cofactor geometry required for Radical, SAM catalysis and sets the stage for the development of inhibitors with, antibacterial function due to the uniquely bacterial occurrence of the, enzyme.

1OLT is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with SAM and SF4 as [http://en.wikipedia.org/wiki/ligands ligands]. Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1OLT OCA].  

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