Review of four major distinct types of human phospholipase A2

Abstract

The phospholipase A₂ superfamily of enzymes plays a significant role in the development and progression of numerous inflammatory diseases. Through their catalytic action on membrane phospholipids, phospholipases are the upstream regulators of the eicosanoid pathway releasing free fatty acids for cyclooxygenases, lipoxygenases, and cytochrome P450 enzymes which produce various well-known inflammatory mediators including leukotrienes, thromboxanes and prostaglandins. Elucidating the association of phospholipases A₂ with the membrane, the extraction and binding of phospholipid substrates, and their interactions with small-molecule inhibitors is crucial for the development of new anti-inflammatory therapeutics. Studying phospholipases has been challenging because they act on the surface of cellular membranes and micelles. Multidisciplinary approaches including hydrogen/deuterium exchange mass spectrometry, molecular dynamics simulations, and other computer-aided drug design techniques have been successfully employed by our laboratory to study interactions of phospholipases with membranes, phospholipid substrates and inhibitors. This review summarizes the application of these techniques to study four human recombinant phospholipases A₂.

Figure 1. Phospholipases A₂ function as degradative enzymes when they produce lysophospholipids and free fatty acids as products, as biosynthetic enzymes when the lysophospholipid product is reacylated with a PUFA to produce important phospholipids, and as signaling enzymes when the products are converted to agonists of GPCRs

(adapted from (Dennis, 2016)).

Figure 2. A model of GVIIA Lp-PLA₂ binding to the surface of a DMPC membrane

The proposed membrane binding region of Lp-PLA₂ is shown in blue (amides 113–120). The proposed region for liposome association (amides 115 and 116) as well as the catalytic triad (Ser273, Asp296, and His351) are shown in red (adapted from (Cao et al., 2011)).

Figure 3. Three-dimensional structure of calcium-independent phospholipase A₂

A homology model of GVIA iPLA₂ is shown (adapted from (Mouchlis et al., 2015)).

Figure 4. Three-dimensional structure of cytosolic phospholipase A₂

The X-ray crystal structure of GIVA cPLA₂ (PDB ID 1CJY) (adapted from (Mouchlis et al., 2015)).

Figure 5. Hypothetical model of GIA sPLA2 before (left) binding to the surface of a DMPC membrane and after (right)

Areas with decreases in deuterium exchange are colored in blue and turquoise (adapted from (Burke et al., 2008)).