4r34

Publication Abstract from PubMed

Streptomyces actuosus tryptophan lyase (NosL) is a radical SAM enzyme which catalyzes the synthesis of 3-methyl-2-indolic acid, a precursor in the synthesis of the promising antibiotic nosiheptide. The reaction involves cleavage of the tryptophan CalphaCbeta bond and recombination of the amino-acid-derived -COOH fragment at the indole ring. Reported herein is the 1.8 A resolution crystal structure of NosL complexed with its substrate. Unexpectedly, only one of the tryptophan amino hydrogen atoms is optimally placed for H abstraction by the SAM-derived 5'-deoxyadenosyl radical. This orientation, in turn, rules out the previously proposed delocalized indole radical as the species which undergoes CalphaCbeta bond cleavage. Instead, stereochemical considerations indicate that the reactive intermediate is a (.) NH tryptophanyl radical. A structure-based amino acid sequence comparison of NosL with the tyrosine lyases ThiH and HydG strongly suggests that an equivalent (.) NH radical operates in the latter enzymes.

Crystal Structure of Tryptophan Lyase (NosL): Evidence for Radical Formation at the Amino Group of Tryptophan.,Nicolet Y, Zeppieri L, Amara P, Fontecilla-Camps JC Angew Chem Int Ed Engl. 2014 Oct 27;53(44):11840-4. doi: 10.1002/anie.201407320. , Epub 2014 Sep 5. PMID:25196319^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.