205
9.2
Anti-inflammatory Molecules-Enzyme Inhibitors
9.2.1 Phospholipase A 2 Inhibitors
During tissue injury, membrane phospholipids get hydrolysed to produce fatty acids
and lysophospholipid through phospholipase A 2 (Farooqui 2000). Hydrolysis follows in the ester linkage of sn-2 position of phospholipids. These metabolites serve
as the precursor for platelet-activating factor (PAF) and eicosanoids, the main
inflammatory mediators, and the reactions represent the rate-limiting step in the
eicosanoid production. More than 19 different isoforms of PLA 2 have been identified in mammalian system. They have been shown to participate in physiological
events related to cell injury, inflammation and apoptosis. PLA 2 was purified first
from cobra venom and later from rattlesnake venom. During 1970, as the proteinsequencing methodologies advanced, sequence was identified and these enzymes
indicated the presence of more cysteine (> 10% of the amino acids) residues.
Mammalian and porcine pancreatic PLA 2 s were identified during the same period
and were found to have the same disulphide bond pattern as that of cobra venom.
In 1988, Jeffery J. Seilhamer and Lorin K. Johnson from California Biotechnology
Inc. and Ruth M. Kramer from Biogen Research Corporation (Dennis et al. 2011)
independently purified and sequenced new human non-pancreatic PLA 2 from synovial fluid and found its disulphide pattern similar to that in rattle snake venom
named as secretory PLA 2 . After that sPLA 2 was isolated and purified from different
cells and designated as sPLA 2 GI, GII, GIII, GV, GIX, GX, GXI, GXII, GXIII and
GXIV. Molecular weights of these enzymes were found to be within 13–15 kDa,
and their catalytic residue contains His/Asp. Later cytosolic PLA 2 was isolated and
purified but its sequences were unrelated to sPLA 2 and reported as GIV having a
molecular weight of 60–224 kDa and catalytic residues include Ser/Asp. Another
cytosolic PLA 2 was identified which is Ca
2+
independent and designated as GVI
found to be 84–90 kDa in molecular weight. A new PLA 2 was isolated from human
plasma that hydrolyses platelet-activating factor and termed as lipoproteinassociated PLA 2 (Dennis et al. 2011). These enzymes have specificity for a short
acyl chain on sn-2 position, and these are labelled as GVII and GVIII. These
enzymes are 20–45 kDa in molecular weight, and their catalytic residue contains
Ser/His/Asp. A new type of PLA 2 was identified from lysosome (GXV) and adipose
tissue (GXVI) with 45 and 18 kDa in molecular weight, and their catalytic site contains Ser/His/Asp and His/Cys, respectively (Burke and Dennis 2009).
9.2.1.1 Structural Characterization of Phospholipase A 2
Secretory PLA 2 is found to contain a catalytic site and a highly conserved Ca
2+
binding loop. All forms of these enzymes share a common protein fold with a slight
difference. They have same catalytic His/Asp dyad and contain three long α-helices
and two β-sheets also (Dennis et al. 2011). Cobra venom PLA 2 is the best studied
PLA 2 , and structural characterization of PLA 2 was explained based on this enzyme.
This enzyme has six conserved disulphide bonds with an additional bond between
11 and 71 residues. Calcium ions bind with carbonyl oxygen of tyrosine and glycine
9 Anti-inflammatory Molecules: Enzyme Inhibitors
9.2
Anti-inflammatory Molecules-Enzyme Inhibitors
9.2.1 Phospholipase A 2 Inhibitors
During tissue injury, membrane phospholipids get hydrolysed to produce fatty acids
and lysophospholipid through phospholipase A 2 (Farooqui 2000). Hydrolysis follows in the ester linkage of sn-2 position of phospholipids. These metabolites serve
as the precursor for platelet-activating factor (PAF) and eicosanoids, the main
inflammatory mediators, and the reactions represent the rate-limiting step in the
eicosanoid production. More than 19 different isoforms of PLA 2 have been identified in mammalian system. They have been shown to participate in physiological
events related to cell injury, inflammation and apoptosis. PLA 2 was purified first
from cobra venom and later from rattlesnake venom. During 1970, as the proteinsequencing methodologies advanced, sequence was identified and these enzymes
indicated the presence of more cysteine (> 10% of the amino acids) residues.
Mammalian and porcine pancreatic PLA 2 s were identified during the same period
and were found to have the same disulphide bond pattern as that of cobra venom.
In 1988, Jeffery J. Seilhamer and Lorin K. Johnson from California Biotechnology
Inc. and Ruth M. Kramer from Biogen Research Corporation (Dennis et al. 2011)
independently purified and sequenced new human non-pancreatic PLA 2 from synovial fluid and found its disulphide pattern similar to that in rattle snake venom
named as secretory PLA 2 . After that sPLA 2 was isolated and purified from different
cells and designated as sPLA 2 GI, GII, GIII, GV, GIX, GX, GXI, GXII, GXIII and
GXIV. Molecular weights of these enzymes were found to be within 13–15 kDa,
and their catalytic residue contains His/Asp. Later cytosolic PLA 2 was isolated and
purified but its sequences were unrelated to sPLA 2 and reported as GIV having a
molecular weight of 60–224 kDa and catalytic residues include Ser/Asp. Another
cytosolic PLA 2 was identified which is Ca
2+
independent and designated as GVI
found to be 84–90 kDa in molecular weight. A new PLA 2 was isolated from human
plasma that hydrolyses platelet-activating factor and termed as lipoproteinassociated PLA 2 (Dennis et al. 2011). These enzymes have specificity for a short
acyl chain on sn-2 position, and these are labelled as GVII and GVIII. These
enzymes are 20–45 kDa in molecular weight, and their catalytic residue contains
Ser/His/Asp. A new type of PLA 2 was identified from lysosome (GXV) and adipose
tissue (GXVI) with 45 and 18 kDa in molecular weight, and their catalytic site contains Ser/His/Asp and His/Cys, respectively (Burke and Dennis 2009).
9.2.1.1 Structural Characterization of Phospholipase A 2
Secretory PLA 2 is found to contain a catalytic site and a highly conserved Ca
2+
binding loop. All forms of these enzymes share a common protein fold with a slight
difference. They have same catalytic His/Asp dyad and contain three long α-helices
and two β-sheets also (Dennis et al. 2011). Cobra venom PLA 2 is the best studied
PLA 2 , and structural characterization of PLA 2 was explained based on this enzyme.
This enzyme has six conserved disulphide bonds with an additional bond between
11 and 71 residues. Calcium ions bind with carbonyl oxygen of tyrosine and glycine
9 Anti-inflammatory Molecules: Enzyme Inhibitors