Structure and mechanism of the Propionibacterium acnes polyunsaturated fatty acid isomerase

Abstract

Conjugated linoleic acids (CLAs) affect body fat gain, carcinogenesis, insulin resistance, and lipid peroxidation in mammals. Several isomers of CLA exist, of which the (9Z, 11E) and (10E, 12Z) isomers have beneficial effects on human metabolism but are scarce in foods. Bacterial polyunsaturated fatty acid isomerases are promising biotechnological catalysts for CLA production. We describe six crystal structures of the Propionibacterium acnes polyunsaturated fatty acid isomerase PAI in apo-and product-bound forms. The three-domain flavoprotein has previously undescribed folds outside the FAD-binding site. Conformational changes in a hydrophobic channel toward the active site reveal a unique gating mechanism for substrate specificity. The geometry of the substratebinding site explains the length preferences for C18 fatty acids. A catalytic mechanism for double-bond isomerization is formulated that may be altered to change substrate specificity for syntheses of rare CLAs from easily accessible precursors.conjugated linoleic acid ͉ flavoprotein ͉ polyenoic fatty acid isomerase ͉ structure-based mechanism

Isomers of conjugated linoleic acids are synthesized via different mechanisms in ruminal digesta and bacteria

“…The isomerase responsible for trans-10,cis-12-CLA formation by a human skin-derived P. acnes has been characterized extensively (13). Trans-10,cis-12-CLA-producing P. acnes isolates have also been isolated from the rumen (33).…”

“…Cloning, crystallization, and structural analysis of the isomerase catalyzing the formation of trans-10,cis-12-CLA by Propionibacterium acnes has revealed the geometry of fatty acid binding to the enzyme and demonstrated a mode of action that involves hydride abstraction by enzyme-bound flavin adenine dinucleotide and the involvement of specific aromatic amino acid residues (13). Comparable information on the enzyme that forms RA is much more rudimentary.…”

Mechanism of conjugated linoleic acid and vaccenic acid formation in human faecal suspensions and pure cultures of intestinal bacteria

“…The CLA isomers formed by human intestinal bacteria contrast even more with those produced during LA metabolism by Lactobacillus plantarum and related species, where trans-9,trans-11-CLA is often the most abundant isomer formed (Ogawa et al, 2001(Ogawa et al, , 2005. P. acnes, by contrast, produces only trans-10,cis-12 CLA (Liavonchanka et al, 2006). The formation of CLA by P. freudenreichii subsp.…”

“…CLA could be formed by a direct isomerization (Liavonchanka et al, 2006), a hydration/dehydration mechanism (Ogawa et al, 2001(Ogawa et al, , 2005, or a hydrogen-abstraction mechanism involving a radical intermediate . From the data presented here and from elsewhere (Liavonchanka et al, 2006;Wallace et al, 2007), it seems clear that 10,12 CLA isomers are formed by an isomerase mechanism that does not involve proton exchange with water. The mechanism of RA formation remains uncertain, however.…”

Linoleic Acid Isomerase inLactobacillus plantarumAKU1009a Proved to Be a Multi-Component Enzyme System Requiring Oxidoreduction Cofactors

“…As for the enzyme involved in trans-10,cis-12-CLA production, the enzyme from Propionibacterium acnes, which has been characterized as a polyunsaturated fatty acid isomerase, 16) was purified, cloned, expressed in E. coli, and crystallized. It was found to be a flavoprotein, and produced only trans-10,cis-12-CLA directly from linoleic acid, without forming any intermediate.…”