TY - JOUR
T1 - Prostaglandin endoperoxide H synthases
T2 - Peroxidase hydroperoxide specificity and cyclooxygenase activation
AU - Liu, Jiayan
AU - Seibold, Steve A.
AU - Rieke, Caroline J.
AU - Song, Inseok
AU - Cukier, Robert I.
AU - Smith, William L.
PY - 2007/6/22
Y1 - 2007/6/22
N2 - The cyclooxygenase (COX) activity of prostaglandin endoperoxide H synthases (PGHSs) converts arachidonic acid and O2 to prostaglandin G 2 (PGG2). PGHS peroxidase (POX) activity reduces PGG 2 to PGH2. The first step in POX catalysis is formation of an oxyferryl heme radical cation (Compound I), which undergoes intramolecular electron transfer forming Intermediate II having an oxyferryl heme and a Tyr-385 radical required for COX catalysis. PGHS POX catalyzes heterolytic cleavage of primary and secondary hydroperoxides much more readily than H2O 2, but the basis for this specificity has been unresolved. Several large amino acids form a hydrophobic "dome" over part of the heme, but when these residues were mutated to alanines there was little effect on Compound I formation from H2O2 or 15- hydroperoxyeicosatetraenoic acid, a surrogate substrate for PGG2. Ab initio calculations of heterolytic bond dissociation energies of the peroxyl groups of small peroxides indicated that they are almost the same. Molecular Dynamics simulations suggest that PGG2 binds the POX site through a peroxyl-iron bond, a hydrogen bond with His-207 and van der Waals interactions involving methylene groups adjoining the carbon bearing the peroxyl group and the protoporphyrin IX. We speculate that these latter interactions, which are not possible with H2O2, are major contributors to PGHS POX specificity. The distal Gln-203 four residues removed from His-207 have been thought to be essential for Compound I formation. However, Q203V PGHS-1 and PGHS-2 mutants catalyzed heterolytic cleavage of peroxides and exhibited native COX activity. PGHSs are homodimers with each monomer having a POX site and COX site. Cross-talk occurs between the COX sites of adjoining monomers. However, no cross-talk between the POX and COX sites of monomers was detected in a PGHS-2 heterodimer comprised of a Q203R monomer having an inactive POX site and a G533A monomer with an inactive COX site.
AB - The cyclooxygenase (COX) activity of prostaglandin endoperoxide H synthases (PGHSs) converts arachidonic acid and O2 to prostaglandin G 2 (PGG2). PGHS peroxidase (POX) activity reduces PGG 2 to PGH2. The first step in POX catalysis is formation of an oxyferryl heme radical cation (Compound I), which undergoes intramolecular electron transfer forming Intermediate II having an oxyferryl heme and a Tyr-385 radical required for COX catalysis. PGHS POX catalyzes heterolytic cleavage of primary and secondary hydroperoxides much more readily than H2O 2, but the basis for this specificity has been unresolved. Several large amino acids form a hydrophobic "dome" over part of the heme, but when these residues were mutated to alanines there was little effect on Compound I formation from H2O2 or 15- hydroperoxyeicosatetraenoic acid, a surrogate substrate for PGG2. Ab initio calculations of heterolytic bond dissociation energies of the peroxyl groups of small peroxides indicated that they are almost the same. Molecular Dynamics simulations suggest that PGG2 binds the POX site through a peroxyl-iron bond, a hydrogen bond with His-207 and van der Waals interactions involving methylene groups adjoining the carbon bearing the peroxyl group and the protoporphyrin IX. We speculate that these latter interactions, which are not possible with H2O2, are major contributors to PGHS POX specificity. The distal Gln-203 four residues removed from His-207 have been thought to be essential for Compound I formation. However, Q203V PGHS-1 and PGHS-2 mutants catalyzed heterolytic cleavage of peroxides and exhibited native COX activity. PGHSs are homodimers with each monomer having a POX site and COX site. Cross-talk occurs between the COX sites of adjoining monomers. However, no cross-talk between the POX and COX sites of monomers was detected in a PGHS-2 heterodimer comprised of a Q203R monomer having an inactive POX site and a G533A monomer with an inactive COX site.
UR - http://www.scopus.com/inward/record.url?scp=34547137409&partnerID=8YFLogxK
U2 - 10.1074/jbc.M701235200
DO - 10.1074/jbc.M701235200
M3 - Article
C2 - 17462992
AN - SCOPUS:34547137409
SN - 0021-9258
VL - 282
SP - 18233
EP - 18244
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 25
ER -