Helical remodeling augments 5-lipoxygenase activity in the synthesis of proinflammatory mediators

Cryo-EM structures of human arachidonate 12S-Lipoxygenase (12-LOX) bound to endogenous and exogenous inhibitors

“…In the 12-LOX dimer, one subunit adopts an “open” conformation while another undergoes significant conformational change involving a large-scale α2 movement. The alterations to the extended α2 conformation were observed previously in crystal structures of stable 5-LOX 12,43–45 (broken or disordered α2) and 15-LOX-1 11,13 (large-scale α2 movement). The 15-LOX-1 and now the 12-LOX are the only LOXs that were captured forming non-symmetrical dimers with one subunit in the “open” and one in the “closed” conformations.…”

Theoretical Study of the Arachidonic Acid Conversion into Leukotriene A4 Catalyzed by Human 5-Lipoxygenase: Hydroperoxidation and Epoxidation Mechanisms and Arachidonic Acid Active Site Access

“…To analyze the structure of an open conformation, a Stable-5-LOX whose crystal structure exhibits a helix α2 elongated (PDB code 7TTJ) has been taken as a model. 20 Indeed, quite apart from the helix α2 and to a lesser extend the helix α18, the overall structure of human-5-LOX is preserved regardless of its conformation. Given that these two helixes are only involved in channel B, it is expected that both channel A and channel C remain practically unaffected, which would imply that their PMFs are still valid.…”

“…The first one would be how the interaction between this enzyme and its helper protein (FLAP) occurs since it is well-known that human-5-LOX reaches its maximum catalytic activity when it acts accompanied by FLAP, whose main role is to supply AA to human-5-LOX from a phospholipid membrane, and in the presence of Ca 2+ , which favors the release of AA. 20 On the other hand, when these two proteins act together, both the N-terminal domain of human-5-LOX and FLAP should be associated with the membrane and at least one entrance to the human-5-LOX cavity should lie close to the AA site in FLAP. Taking all this into account and according to the calculated channels, the most feasible way of interaction between human-5-LOX and FLAP is by means of the human-5-LOX side in which the helix α2 lies, since the Nterminal domain of human-5-LOX would point toward FLAP, and therefore toward the phospholipid membrane, and channel B would lie close to the AA site in FLAP.…”

“…When cells are stimulated to release intracellular Ca 2+ , the translocation of cytosolic phospholipase A 2 and 5-LOX to the nuclear membrane is triggered. Phospholipase A 2 mediates the release of AA from membrane phospholipids, and a small membrane protein, 5-lipoxygenase-activating protein (FLAP) transfers AA to 5-LOX. ,, It has been proposed , that the open conformation would increase the ability of 5-LOX to convert 5-HpETE into LTA 4 and that this conformation is likely the one presented by 5-LOX when interacting with membrane-embedded FLAP. On the other hand, human-5-LOX can also produce LTA 4 in vitro (in the absence of the membrane-embedded FLAP) from AA sequentially (hydroperoxidation + epoxidation) …”

“…An elongated helix α2 with at least six turns appears in the LOX isoforms in animals, but in Stable 5-LOX, it is a broken helix with segments of at most three-helical turns that form a v-like structure. With this position of the helix α2 the aromatic side chains of the residues Tyr181 and Phe177 cork the cavity at one end of the elongated cavity, , thus obstructing the way of AA into the active site. It is called a closed conformation, in contrast to the elongated, open conformation of the helix α2 in other animal LOXs.…”