Membrane Association Allosterically Regulates Phospholipase A₂ Enzymes and Their Specificity

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Water-soluble proteins as well as membrane-bound proteins associate with membrane surfaces and bind specific lipid molecules in specific sites on the protein. Membrane surfaces include the traditional bilayer membranes of cells and subcellular organelles formed by phospholipids. Monolayer membranes include the outer monolayer phospholipid surface of intracellular lipid droplets of triglycerides and various lipoproteins including HDL, LDL, VLDL, and chylomicrons. These lipoproteins circulate in our blood and lymph systems and contain triglycerides, cholesterol, cholesterol esters, and proteins in their interior, and these are sometimes interspersed on their surfaces. Similar lipid−water interfaces also occur in mixed micelles of phospholipids and bile acids in our digestive system, which may also include internalized triglycerides and cholesterol esters. Diacyl phospholipids constitute the defining molecules of biological membranes. Phospholipase A 1 (PLA 1 ) hydrolyzes phospholipid acyl chains at the sn-1 position of membrane phospholipids, phospholipase A 2 (PLA 2 ) hydrolyzes acyl chains at the sn-2 position, phospholipase C (PLC) hydrolyzes the glycerol−phosphodiester bond, and phospholipase D (PLD) hydrolyzes the polar group−phosphodiester bond. Of the phospholipases, the PLA 2 s have been the most well studied at the mechanistic level. The PLA 2 superfamily consists of 16 groups and numerous subgroups, and each is generally described as one of 6 types. The most well studied of the PLA 2 s include extensive genetic and mutational studies, complete lipidomics specificity characterization, and crystallographic structures. This Account will focus principally on results from deuterium exchange mass spectrometric (DXMS) studies of PLA 2 interactions with membranes and extensive molecular dynamics (MD) simulations of their interactions with membranes and specific phospholipids bound in their catalytic and allosteric sites. These enzymes either are membrane-bound or are water-soluble and associate with membranes before extracting their phospholipid substrate molecule into their active site to carry out their enzymatic hydrolytic reaction. We present evidence that when a PLA 2 associates with a membrane, the membrane association can result in a conformational change in the enzyme whereby the membrane association with an allosteric site on the enzyme stabilizes the enzyme in an active conformation on the membrane. We sometimes refer to this transition from a "closed" conformation in aqueous solution to an "open" conformation when associated with a membrane. The enzyme can then extract a single phospholipid substrate into its active site, and catalysis occurs. We have also employed DXMS and MD simulations to characterize how PLA 2 s interact with specific inhibitors that could lead to potential therapeutics. The PLA 2 s constitute a paradigm for how membranes interact allosterically with proteins, causing conformational changes and activation of the proteins to enable t...

Modulation of Phospholipase A2 Membrane Activity by Anti-inflammatory Drugs

“…On the other hand, it has been reported that when a PLA 2 exerts its action on a lipid membrane, the enzyme stabilizes, going from a “closed” conformation in the aqueous solution to an “open” one within the membrane . Clearly, such an allosteric regulation of PLA2 activity is intrinsically related to our findings, where AIDs perform specific lipid remodeling to delay or catalyze lipid cleavage.…”

“…31 On the other hand, it has been reported that when a PLA 2 exerts its action on a lipid membrane, the enzyme stabilizes, going from a "closed" conformation in the aqueous solution to an "open" one within the membrane. 70 Clearly, such an allosteric regulation of PLA2 activity is intrinsically related to our findings, where AIDs perform specific lipid remodeling to delay or catalyze lipid cleavage. Additionally, it has also demonstrated a chain length dependence (membrane packing) of PLA 2 activity, 51 by which we speculate that different acyl chains might undergo the same opposite behavior as in Figure 2d, although to different extents.…”

Regulatory mechanisms triggered by enzyme interactions with lipid membrane surfaces

“…The Dennis lab ( Dennis, 2022 ; Mouchlis and Dennis, 2022 ) has made many important insights into the allosteric interaction between lipid bilayer membranes and PLA 2 , especially through their judicial use of hydrogen–deuterium exchange mass spectrometry (HDX-MS) combined with MD simulations to understand the association mechanism of the recombinant human form of group IVA cytosolic (cPLA 2 ), group V secreted (sPLA 2 ), group VIA calcium-independent (iPLA 2 ), and group VIIA lipoprotein-associated phospholipase A 2 (GVIIA Lp-PLA 2 ); they propose that PLA 2 exists in at least three forms: the “closed” form in the cytosol, the “open” membrane-associated “unbound” form, and the “open” membrane-associated “bound” form when binding to a substrate ( Mouchlis and Dennis, 2022 ).…”

Lipid Changes in the Peri-Implantation Period with Mass Spectrometry Imaging: A Systematic Review

“…The fatty acids that comprise phospholipids often differ only in the localization of the single unsaturated bond (e.g., C18:1n-7 or C18:1n-9) or in the conformation of the unsaturated bond (cis and trans isomers of C18:1n-9: cis oleic acid and trans elaidic acid). A further problem is that the MSI technique does not provide information on the relative position (sn-1 or sn-2) of the fatty acids to the glycerol backbone, although the position of the fatty acid is biochemically very important [ 21 , 22 ]. Another limitation is the relatively low spatial resolution of these conventional MSI methods with pixel sizes between 30 and 100 μm [ 23 ].…”