PLA2

Phospholipase A2 (PLA2) is based on the distribution of Ca²⁺ -dependent PLA2 in the body. Can be divided into secretory type (PLA2-Ⅰ and PLA2-Ⅱ) and cytoplasmic type (PLA2-Ⅲ and PLA2-Ⅳ). PLA2-Ⅱ is an early marker of a series of complications in severe pancreatitis. As an acute phase reaction medium, it is closely related to the development of severe pancreatitis. Therefore, the determination of PLA2-Ⅱ has an important recognition effect on bacterial infectious necrotizing pancreatitis and severe AP complicated with multiple organ failure.

Figure 1. Protein structure of PLA2.

Introductions

Phospholipase A2 (phospholipaseA2 PLA2) is a hydrolase that can catalyze the acyl group on the phospholipid glycerol molecule. It is also the rate-limiting rate for the production of biologically active substances such as arachidonic acid (AA), prostaglandin and platelet activating factor (PAF) enzymes, the resulting lipid mediators play a key role in the activation of membrane channels, information transmission, hemodynamics and pathophysiology during inflammation and tissue damage, as well as in regulating intracellular and extracellular metabolism. In patients with acute pancreatitis, septic shock, trauma, and multiple organ failure (MSOF), serum PLA2 activity is increased. In multiple trauma, changes in PLA2 activity may be the early signaling parameters that lead to MSOF tissue damage.

Figure 2. Chemical structure of arachidonic acid (AA).

PLA2 source distribution

Almost all human cells contain PLA2, mainly in two subcellular distributions, one is membrane-bound PLA2 (Ma-PLA2), the other is lysosome and soluble PLA2 in cytosol (S-PLA2). Mammal extracellular PLA2 is a normal physiological secretion. The pancreas, salivary glands, prostate, and seminal vesicles can secrete S-PLA2; activated monocytes, macrophages, and neutrophils secrete a large amount of PLA2 and become PLA2 in body fluids The main source of S-PLA2 secretion into tissue fluid, peritoneal fluid, synovial fluid and subcutaneous tissue, leading to a variety of inflammatory and pathological damage in experiments and clinics, through sensitive, simple and fast PLA2 measurement, can be used as an early predictor of pathological progress and diagnosis Sexual index. Ma-PLA2 exists on the biofilm of various cells, especially in brain cells, cardiomyocytes, hepatocytes, mesangial cells and alveoli. It is involved in the conversion of cell membrane phospholipids, AA metabolism and chemotaxis under physiological conditions role, mitosis, cytotoxicity, and stimulatory release coupling; under pathological conditions, lysosomes and mitochondrial PLA2 are secreted into the interstitium, joint cavity, or vascular space, and participate in the pathogenesis of inflammation and acute injury.

Functions

Phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 position of membrane glycerophospholipids to liberate arachidonic acid (AA), a precursor of eicosanoids including prostaglandins (PGs) and leukotrienes (LTs). The same reaction also produces lysophosholipids, which represent another class of lipid mediator. So far, at least 19 enzymes that possess PLA2 activity have been identified in mammals. The secretory PLA2 (sPLA2) family, in which 10 isozymes have been identified, consists of low-molecular-weight, Ca²⁺-requiring, secretory enzymes that have been implicated in a number of biological processes, such as modification of eicosanoid generation, inflammation, host defense, and atherosclerosis. The cytosolic PLA2 (cPLA2) family consists of 3 enzymes, among which cPLA2alpha plays an essential role in the initiation of AA metabolism. Intracellular activation of cPLA2alpha is tightly regulated by Ca2+ and phosphorylation. The Ca2+-independent PLA2 (iPLA2) family contains 2 enzymes and may play a major role in membrane phospholipid remodeling. The platelet-activating factor (PAF) acetylhydrolase (PAF-AH) family represents a unique group of PLA2 that contains 4 enzymes exhibiting unusual substrate specificity toward PAF and/or oxidized phospholipids.

Figure 3. Chemical structure of prostaglandins.

Conclusions

Phospholipase A2 is one of the most thoroughly studied membrane proteins. It hydrolyzes phospholipids at the sn-2 position to form fatty acid and lysophospholipid products. These are small proteins, and for certain species, high-resolution 3-D structures are well known. Phospholipase A2 proteins are highly medicinal because they are responsible for the release of arachidonic acid from the membrane, and due to the subsequent conversion of this fatty acid to leukotrienes and prostaglandins are part of the inflammatory response.The enzyme also showed very interesting interactions with the membrane it binds. When it interacts with the aggregated form of the matrix (such as micelles or double layers), it will be activated in some way. It is suspected that electrostatic and hydrophobic interactions are related to the binding of enzymes to the membrane. Little is known about the structure of the enzyme-membrane complex and why the enzyme once binds its substrate in a bound form, and why the enzyme reaction is more efficient.

Figure 4. Membrane protein.

Reference

1. Murakami, M, et al. Phospholipase A2. Journal of Biochemistry. 2002, 131(3), 285–292.