Structural and mechanistic insights into 5-lipoxygenase inhibition by natural products

Abstract

Leukotrienes (LT) are lipid mediators of the inflammatory response that are linked to asthma and atherosclerosis. LT biosynthesis is initiated by 5-lipoxygenase (5-LOX) with the assistance of the substrate-binding 5-LOX-activating protein at the nuclear membrane. Here, we contrast the structural and functional consequences of the binding of two natural product inhibitors of 5-LOX. The redox-type inhibitor nordihydroguaiaretic acid (NDGA) is lodged in the 5-LOX active site, now fully exposed by disordering of the helix that caps it in the apo-enzyme. In contrast, the allosteric inhibitor 3-acetyl-11-keto-beta-boswellic acid (AKBA) from frankincense wedges between the membrane-binding and catalytic domains of 5-LOX, some 30 Å from the catalytic iron. While enzyme inhibition by NDGA is robust, AKBA promotes a shift in the regiospecificity, evident in human embryonic kidney 293 cells and in primary immune cells expressing 5-LOX.

Potential of pyrroquinazoline alkaloids fromAdhatoda vasicaNees. as inhibitors of 5-LOX – a computational and anin-vitrostudy

“…This supports the in-silico results that indicate that VAE with a favourable binding energy of À8.33 kcal/mol is a potent competitive inhibitor that sits on top of Fe 2þ and below the F-Y cork region, possibly blocking the access of AA to the Fe 2þ . This is similar to the inhibition exhibited by NDGA (Nordihydroguaiaretic acid) that blocks access of the substrate to the catalytic centre by sitting between the F-Y cork (Gilbert et al, 2020). It is also worth noting that NDGA and VAE share interactions with five common key residues GLN 363, LEU 368, HD2 372, ILE 406 and ALA 410 further strengthening the VAE's capability as a potential competitive inhibitor.…”

Fatty Acid Allosteric Regulation of C-H Activation in Plant and Animal Lipoxygenases

“…This model is further supported by a recent structure of human 5-LOX bound to an isoform-selective allosteric effector, AKBA (3-acetyl-11-keto-beta-boswellic acid), that alters the substrate regio-specificity of the enzyme [38]. The AKBA molecule was seen to associate at the interface of the PLAT and catalytic domains in h5-LOX.…”

“…The location of this “cork” in h5-LOX is near the position of the π-helix in SLO-1 ( Figure 2 D). It has been suggested that, in order for a substrate to bind, helix 2 of h5-LOX must undergo a conformational change [ 37 , 38 ]. As observed by mutagenesis, the bulk of tyrosine at position 181 may provide the “cork” to limit substrate entrance, as substitution of Y181 for alanine enhances catalytic proficiency threefold [ 39 ].…”

“…The helix 2 (residues 169–201) of h5-LOX in this model features a short three turn helix flanked by loops, whereas the helix 2 elements of h15-LOX-2 and SLO-1 are comprised of contiguous six to seven turn helices ( Figure 2 D). A recent structure of an inhibitor h5-LOX complex [ 38 ] revealed uninterpretable electron density for residues 173–214, including a significant portion of helix 2. Together, the results were interpreted in the context of an inhibitor-induced (or ligand-induced) change in helix 2 conformation.…”

“…By extension, the N-terminal PLAT domain in plant and animal LOXs has been suggested to be involved in membrane association. Though the structures of h5-LOX do not have Ca 2+ bound ( Figure 2 C) [ 37 , 38 ], there is strong evidence to support calcium-dependent membrane binding. Cellular experiments, in which the N-terminal β-barrel of human 5-LOX was expressed independently of the catalytic domain, established the localization of the PLAT domain to the lipid membrane [ 47 ].…”