206
from calcium-binding loop as well as conserved aspartic acid residues. Calcium is
required for the hydrolysis of the sn-2 carbonyl oxygen and coordinates with a catalytic water molecule. Crystal structures of PLA 2 reveal that only about 9–10 carbon
of sn-2 acyl chain interacts with enzyme and rest of the chains are buried within the
lipid–water interface. The hydrophobic residues like Leu2, Phe5, Trp19, Tyr52 and
Tyr69 wrap around the acyl chain of the lipid substrate (Gelb et al. 1994).
PLA 2 activity is based on the interaction of the protein with large lipid aggregates. The presence of aromatic residues, mainly the tryptophan residue, contributes
to the interfacial binding surface which assists the hydrolysis of zwitterionic phospholipids. As suggested, catalytic mechanism of PLA 2 is introduced by His48/
Asp99/calcium complex within the active site. Bridging of the second water molecule by His48 is the basis of nucleophilicity. The basicity of His48 is enhanced
through hydrogen bonding with Asp99. Since the asparagine amide group can function to lower the pKa of the bridging water molecule, substitution of asparagine
with His48 can maintain wild-type activity. Calcium-coordinated oxy-anion composed of tetrahedral intermediate degradation is the rate-limiting stage. Relatively
small cations like nickel or cobalt may duplicate the role of calcium.
9.2.1.2 Disease Implication of PLA 2
The sPLA 2 s have significant role in several inflammatory diseases. Patients suffering
from osteoarthritis, rheumatoid arthritis, crystal-associated arthritis, acute pancreatitis (Dennis et al. 2011), septic shock, Crohn’s diseases, adult respiratory distress
syndrome (ARDS), inflammatory bowel disease, atherosclerosis and ulcerative colitis showed an increased amount of GII sPLA 2 in their synovial fluid. PLA 2 also has a
role in tumourigenesis and increased expression found in prostate cancer, breast cancer and in neoplastic prostatic and gastric adenocarcinomas (Dennis et al. 2011).
9.2.1.3 Synthetic Inhibitors of PLA 2
Many PLA 2 inhibitors have been obtained and described from natural and synthetic
sources. Initially, phospholipid analogues were synthesized and used as inhibitors in
studies and here we describe a series of synthetic compounds under investigation.
1-Stearyl-2-stearoylaminodeoxy phosphatidylcholine (Fig. 9.2a) was studied and
found to be a reversible inhibitor of PLA 2 from cobra venom (Naja naja) (Davidson
et al. 1986). At the same time, long chain difluoro ketone analogues were also studied. In the series of phosphatidyl ethanolamine modifications, a thioether amide of
PE was found to be a potent inhibitor (Fig. 9.2b). An acyl amino analogue (Fig. 9.2c)
of phospholipids was developed at the same time as an inhibitor of porcine pancreatic PLA 2 (De Haas et al. 1989). A class of phosphonate analogue of phospholipid
was found to be a tight inhibitor of the same enzyme while acyl amino analogue of
phospholipid was developed as an inhibitor of porcine PLA 2 .
Dicarboxylic acid derivatives (BMS-181162) (Tramposch et al. 1992) are found
to be specific inhibitors of 14 KDa PLA 2 to block arachidonic acid release and biosynthesis of LTB 4 and PAF in calcium ionophore-stimulated human PMNs with an
IC 50 of 10 μM (Dennis et al. 2011). Another derivative BMS 188184 (Tramposch
et al. 1994) has better stability and inhibits human non-pancreatic PLA 2 with an IC 50
of 17 μM and reduces mouse ear oedema with an ED 50 = 9.37 μg/ear (Fig. 9.3).
C.S. Sharanya and M. Haridas
from calcium-binding loop as well as conserved aspartic acid residues. Calcium is
required for the hydrolysis of the sn-2 carbonyl oxygen and coordinates with a catalytic water molecule. Crystal structures of PLA 2 reveal that only about 9–10 carbon
of sn-2 acyl chain interacts with enzyme and rest of the chains are buried within the
lipid–water interface. The hydrophobic residues like Leu2, Phe5, Trp19, Tyr52 and
Tyr69 wrap around the acyl chain of the lipid substrate (Gelb et al. 1994).
PLA 2 activity is based on the interaction of the protein with large lipid aggregates. The presence of aromatic residues, mainly the tryptophan residue, contributes
to the interfacial binding surface which assists the hydrolysis of zwitterionic phospholipids. As suggested, catalytic mechanism of PLA 2 is introduced by His48/
Asp99/calcium complex within the active site. Bridging of the second water molecule by His48 is the basis of nucleophilicity. The basicity of His48 is enhanced
through hydrogen bonding with Asp99. Since the asparagine amide group can function to lower the pKa of the bridging water molecule, substitution of asparagine
with His48 can maintain wild-type activity. Calcium-coordinated oxy-anion composed of tetrahedral intermediate degradation is the rate-limiting stage. Relatively
small cations like nickel or cobalt may duplicate the role of calcium.
9.2.1.2 Disease Implication of PLA 2
The sPLA 2 s have significant role in several inflammatory diseases. Patients suffering
from osteoarthritis, rheumatoid arthritis, crystal-associated arthritis, acute pancreatitis (Dennis et al. 2011), septic shock, Crohn’s diseases, adult respiratory distress
syndrome (ARDS), inflammatory bowel disease, atherosclerosis and ulcerative colitis showed an increased amount of GII sPLA 2 in their synovial fluid. PLA 2 also has a
role in tumourigenesis and increased expression found in prostate cancer, breast cancer and in neoplastic prostatic and gastric adenocarcinomas (Dennis et al. 2011).
9.2.1.3 Synthetic Inhibitors of PLA 2
Many PLA 2 inhibitors have been obtained and described from natural and synthetic
sources. Initially, phospholipid analogues were synthesized and used as inhibitors in
studies and here we describe a series of synthetic compounds under investigation.
1-Stearyl-2-stearoylaminodeoxy phosphatidylcholine (Fig. 9.2a) was studied and
found to be a reversible inhibitor of PLA 2 from cobra venom (Naja naja) (Davidson
et al. 1986). At the same time, long chain difluoro ketone analogues were also studied. In the series of phosphatidyl ethanolamine modifications, a thioether amide of
PE was found to be a potent inhibitor (Fig. 9.2b). An acyl amino analogue (Fig. 9.2c)
of phospholipids was developed at the same time as an inhibitor of porcine pancreatic PLA 2 (De Haas et al. 1989). A class of phosphonate analogue of phospholipid
was found to be a tight inhibitor of the same enzyme while acyl amino analogue of
phospholipid was developed as an inhibitor of porcine PLA 2 .
Dicarboxylic acid derivatives (BMS-181162) (Tramposch et al. 1992) are found
to be specific inhibitors of 14 KDa PLA 2 to block arachidonic acid release and biosynthesis of LTB 4 and PAF in calcium ionophore-stimulated human PMNs with an
IC 50 of 10 μM (Dennis et al. 2011). Another derivative BMS 188184 (Tramposch
et al. 1994) has better stability and inhibits human non-pancreatic PLA 2 with an IC 50
of 17 μM and reduces mouse ear oedema with an ED 50 = 9.37 μg/ear (Fig. 9.3).
C.S. Sharanya and M. Haridas