Molecular determinants of bacterial sensitivity and resistance to mammalian Group IIA phospholipase A2

Abstract

Group IIA secretory phospholipase A2 (sPLA2-IIA) of mammalian species is unique among the many structurally and functionally related mammalian sPLA2 in their high net positive charge and potent (nM) antibacterial activity. Toward the Gram-positive bacteria tested thus far, the global cationic properties of sPLA2-IIA are necessary for optimal binding to intact bacteria and penetration of the multi-layered thick cell wall, but not for the degradation of membrane phospholipids that is essential for bacterial killing. Various Gram-positive bacterial species can differ as much as 1000-fold in sPLA2-IIA sensitivity despite similar intrinsic enzymatic activity of sPLA2-IIA toward the membrane phospholipids of the various bacteria. D-alanylation of wall- and lipo-teichoic acids in Stapylococcus aureus and sortase function in Streptococcus pyogenes increase bacterial resistance to sPLA2-IIA by up to 100-fold apparently by affecting translocation of bound sPLA2-IIA to the cell membrane. Action of the sPLA2-IIA and other related sPLA2 against Gram-negative bacteria is more dependent on cationic properties of the enzyme near the amino-terminus of the protein and collaboration with other host defense proteins that produce alterations of the unique Gram-negative bacterial outer membrane that normally represents a barrier to sPLA2-IIA action.

Secreted PLA2 group X orchestrates innate and adaptive immune responses to inhaled allergen

“…Since we have previously demonstrated that the sPLA 2 -X enzyme is increased in the airways of individuals with asthma (1, 2) and is increased with allergen challenge in humans and in mice, the homeostatic function of the enzyme should be considered, as lipid mediators have both pro-and antiinflammatory effects and the hydrolysis of membranes can directly lead to cell cytotoxicity. For example, other sPLA 2 s such as sPLA 2 -IIA, which we have also found to be elevated in the airways of asthmatics (3), have high activity against gram-positive bacteria due in part to its high net-positive charge, allowing for penetration of the bacterial cell wall (63,64). Although many of the sPLA 2 s have antibacterial properties, sPLA 2 -X is relatively unique because it acts strongly on the outer cell membrane of mammalian cells (65) and is generally thought to have less of a role on direct bacterial cytotoxicity (66).…”

The phospholipid-repair system LplT/Aas in Gram-negative bacteria protects the bacterial membrane envelope from host phospholipase A2 attack

“…sPLA 2 act most efficiently by binding to PL-rich interfaces from which individual PL molecules can diffuse into the active site pocket of the bound enzyme, be degraded, and the products replaced by another PL substrate molecule from this interface (namely interfacial activation mechanism) (14,18). sPLA 2 , especially Group IIA, can penetrate through the cell wall of Grampositive bacteria to directly bind to the membrane, resulting in the high susceptibility of many Grampositive species (3). In contrast, Gram-negative bacteria exhibit much greater intrinsic resistance to sPLA 2 , which has been attributed to the unique structure of their additional outer envelope layer, the outer membrane (OM) (3,19).…”

“…sPLA 2 , especially Group IIA, can penetrate through the cell wall of Grampositive bacteria to directly bind to the membrane, resulting in the high susceptibility of many Grampositive species (3). In contrast, Gram-negative bacteria exhibit much greater intrinsic resistance to sPLA 2 , which has been attributed to the unique structure of their additional outer envelope layer, the outer membrane (OM) (3,19). The OM of Gram-negative bacteria is arranged with an asymmetric lipid distribution: phospholipids (mainly phosphatidylethanolamine, PE) comprise the inner leaflet of the membrane, while the outer leaflet contains the complex glycolipid lipopolysaccharide (LPS).…”

“…secretory phospholipases A 2 (sPLA 2 ) can act directly against many Gram-positive bacteria and against both Gram-positive and Gram-negative bacteria when present in concert with other cellular and humoral host defense systems (3)(4)(5)(6)(7)(8)(9)(10). sPLA 2 catalyze the breakdown of membrane phospholipid (PL) by hydrolyzing the acyl ester bond at the sn-2 position, generating free fatty acid and detergent-like lysophospholipid (LPL) (11).…”

“…sPLA 2 are present in various tissues, tears, and inflammatory fluids, including at high levels in blood plasma of patients with acute bacterial infections. Among the family of ten different sPLA 2 in humans, the Group IIA isoform (sPLA 2 -IIA) is considered the most potent antibacterial sPLA 2 (3,10,(12)(13)(14)(15). However, under at least certain circumstances (e.g., combined action with membrane attack complex (MAC)), other sPLA 2 including the "pancreatic" sPLA 2 -IB can also act on Gram-negative bacteria and contribute to host antibacterial action (6,13,16,17).…”