Lipoprotein-associated phospholipase A ₂ : A paradigm for allosteric regulation by membranes

Abstract

Lipoprotein-associated phospholipase A2 (Lp-PLA2) associates with low- and high-density lipoproteins in human plasma and specifically hydrolyzes circulating oxidized phospholipids involved in oxidative stress. The association of this enzyme with the lipoprotein’s phospholipid monolayer to access its substrate is the most crucial first step in its catalytic cycle. The current study demonstrates unequivocally that a significant movement of a major helical peptide region occurs upon membrane binding, resulting in a large conformational change upon Lp-PLA2 binding to a phospholipid surface. This allosteric regulation of an enzyme’s activity by a large membrane-like interface inducing a conformational change in the catalytic site defines a unique dimension of allosterism. The mechanism by which this enzyme associates with phospholipid interfaces to select and extract a single phospholipid substrate molecule and carry out catalysis is key to understanding its physiological functioning. A lipidomics platform was employed to determine the precise substrate specificity of human recombinant Lp-PLA2 and mutants. This study uniquely elucidates the association mechanism of this enzyme with membranes and its resulting conformational change as well as the extraction and binding of specific oxidized and short acyl-chain phospholipid substrates. Deuterium exchange mass spectrometry coupled with molecular dynamics simulations was used to define the precise specificity of the subsite for the oxidized fatty acid at the sn-2 position of the phospholipid backbone. Despite the existence of several crystal structures of this enzyme cocrystallized with inhibitors, little was understood about Lp-PLA2‘s specificity toward oxidized phospholipids.

Regulation of plasmalogen metabolism and traffic in mammals: The fog begins to lift

“…Functioning of PAF, a pleiotropic factor in many cellular processes including inflammation and the best-described member of the PC[O] class ( Demopoulos et al, 1979 ), is regulated by hydrolysis of the acetyl residue at sn -2 leading to its deactivation. It was shown that this specific deacetylation step is accomplished by PAF acetylhydrolase (also known as lipoprotein-associated PLA 2 ) ( Tjoelker et al, 1995 ; Mouchlis et al, 2022 ). Also, 1- O -alkyl and 1- O -alkenyl ether phospholipids have been proposed to be remodeled by a CoA-independent transacylase, which specifically transfers polyunsaturated C20- and C22-fatty acids ( Fleming and Hajra, 1977 ; Sugiura et al, 1987 ) explaining the finding that ether-linked phospholipid species specifically accumulate PUFA at their sn -2 position.…”

A Dynamic Model for Estimating the Interaction of ROS–PUFA–Antioxidants in Rabbit

“…After oxidation, they are cleaved by phospholipase and released in the interstitial fluids. Consequently, IsoNeuroPs are found in the plasma and can be eliminated through phospholipase A2 [44] with urine (IsoNeuro excretion; Equation ( 6)) at a specific excretion rate (kIsoNeuro excretion). Their concentrations and autoxidation (AutoOx; Equation ( 7)) are assumed to depend on PUFA precursors and/or ROS (kIsoNeuroPs).…”

Phosphatidylcholine Cation—Tyrosine π Complexes: Motifs for Membrane Binding by a Bacterial Phospholipase C

“…The Dennis group has pioneered the concept that the membrane binding of several phospholipase A 2 enzymes allosterically leads to an open conformation of the active site [ 30 , 31 ]. In fact, their recent computational and experimental study of lipoprotein-associated phospholipase A 2 provides evidence that the membrane binding of the protein promotes a conformational change that opens access to the active site [ 32 ]. In contrast, in an aqueous environment, the positioning of a phospholipid in the active site is much less favorable.…”