This (alpha,alpha)6 barrel fold domain is found in linalool dehydratase/isomerase (Ldi) EC:4.2.1.127 . An enzyme found in the betaproteobacterium Castellaniella defragrans 65Phen that mineralizes monoterpenes coupled to anaerobic denitrification. The periplasmic enzyme reversibly catalyzes the isomerisation from the primary alkenol geraniol into the tertiary alkenol (S)-linalool and its dehydration to beta-myrcene. Each monomer is built up of a classical (alpha,alpha)6 barrel fold composed of six inner helices. Structural data of Ldi revealed the terpene binding site between two monomers inside a hydrophobic channel, and three catalytic clusters involved in catalysis [1].

1: Structural and functional insights into asymmetric enzymatic dehydration of alkenols. Nestl BM, Geinitz C, Popa S, Rizek S, Haselbeck RJ, Stephen R, Noble MA, Fischer MP, Ralph EC, Hau HT, Man H, Omar M, Turkenburg JP, van Dien S, Culler SJ, Grogan G, Hauer B; Nat Chem Biol. 2017;13:275-281. PMID:28068311