Identification of Mu-class glutathione transferases M2-2 and M3-3 as cytosolic prostaglandin E synthases in the human brain

Cytosolic prostaglandin (PG) E synthase was purified from human brain corte x. The N-terminal amino acid sequence, PMTLGYXNIRGL, was identical to that of the human mu-class glutathione transferase (GST) M2 subunit. Complementa ry DNAs for human GSTM2, GSTM3, and GSTM4 subunits were cloned, and recombi nant proteins were expressed as homodimers in Escherichia coli. The recombi nant GSTM2-2 and 3-3 catalyzed the conversion of PGH(2) to PGE(2) at the ra tes of 282 and 923 nmol/min/mg of protein, respectively, at the optimal pH of 8, whereas GSTM4-4 was inactive; although all three enzymes showed GST a ctivity. The PGE synthase activity depended on thiols, such as glutathione, dithiothreitol, 2-mercaptoethanol, or L-cysteine. Michaelis-Menten constan ts and turnover numbers for PGH2 were 141 mu M and 10.8 min(-1) for GSTM2-2 and 1.5 mM and 130 min(-1) for GSTM3-3, respectively. GSTM2-2 and 3-3 may play crucial roles in temperature regulation, nociception, and sleep-wake r egulation by producing PCE2 in the brain.