TY - JOUR
T1 - Structural determinants of aromatase cytochrome p450 inhibition in substrate recognition site-1
AU - Conley, Alan J
AU - Mapes, Samantha
AU - Jo Corbin, C.
AU - Greger, Douglas
AU - Graham, Sandra
PY - 2002/1/1
Y1 - 2002/1/1
N2 - The porcine gonadal form of aromatase cytochrome P450 (P450arom) exhibits higher sensitivity to inhibition by the imidazole, etomidate, than the placental isozyme. The residue(s) responsible for this functional difference was mapped using chimeragenesis and point mutation analysis of the placental isozyme, and the kinetic analysis was conducted on native and mutant enzymes after overexpression in insect cells. The etomidate sensitivity of the placental isozyme was markedly increased by substitution of the predicted substrate recognition site-1 (SRS-1) and essentially reproduced that of the gonadal isozyme by substitution of SRS-1 and the predicted B helix. A single isoleucine (I) to methionine (M) substitution at position 133 of the placental isozyme (I133M) was proven to be the criticai residue within SRS-1. Residue 133 is located in the B′-C loop and has been shown to be equally important in other steroid-metabolizing P450s. Single point mutations (including residues 110, 114, 120, 128, 137, and combinations thereof among others) and mutation of the entire B and C helixes were without marked effect on etomidate inhibitory sensitivity. The same mutation (I133M) introduced into human P450arom also markedly increased etomidate sensitivity. Mutation of Ile133 to either alanine (I133A) or tyrosine (I133Y) decreased apparent enzyme activity, but the I133A mutant was sensitive to etomidate inhibition, suggesting that it is Ile133 that decreases etomidate binding rather than Met133 increasing enzyme sensitivity. Androstenedione turnover and affinity were similar for the I133M mutant and the native placental isozyme. These data suggest that Ile133 is a contact residue in SRS-1 of P450arom, emphasize the functional conservation that exists in SRS-1 of a number of steroid-hydroxylating P450 enzymes, and suggest that substrate and inhibitor binding are dependent on different contact points to varying degrees.
AB - The porcine gonadal form of aromatase cytochrome P450 (P450arom) exhibits higher sensitivity to inhibition by the imidazole, etomidate, than the placental isozyme. The residue(s) responsible for this functional difference was mapped using chimeragenesis and point mutation analysis of the placental isozyme, and the kinetic analysis was conducted on native and mutant enzymes after overexpression in insect cells. The etomidate sensitivity of the placental isozyme was markedly increased by substitution of the predicted substrate recognition site-1 (SRS-1) and essentially reproduced that of the gonadal isozyme by substitution of SRS-1 and the predicted B helix. A single isoleucine (I) to methionine (M) substitution at position 133 of the placental isozyme (I133M) was proven to be the criticai residue within SRS-1. Residue 133 is located in the B′-C loop and has been shown to be equally important in other steroid-metabolizing P450s. Single point mutations (including residues 110, 114, 120, 128, 137, and combinations thereof among others) and mutation of the entire B and C helixes were without marked effect on etomidate inhibitory sensitivity. The same mutation (I133M) introduced into human P450arom also markedly increased etomidate sensitivity. Mutation of Ile133 to either alanine (I133A) or tyrosine (I133Y) decreased apparent enzyme activity, but the I133A mutant was sensitive to etomidate inhibition, suggesting that it is Ile133 that decreases etomidate binding rather than Met133 increasing enzyme sensitivity. Androstenedione turnover and affinity were similar for the I133M mutant and the native placental isozyme. These data suggest that Ile133 is a contact residue in SRS-1 of P450arom, emphasize the functional conservation that exists in SRS-1 of a number of steroid-hydroxylating P450 enzymes, and suggest that substrate and inhibitor binding are dependent on different contact points to varying degrees.
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U2 - 10.1210/mend.16.7.0876
DO - 10.1210/mend.16.7.0876
M3 - Article
C2 - 12089342
AN - SCOPUS:85047685695
VL - 16
SP - 1456
EP - 1468
JO - Molecular Endocrinology
JF - Molecular Endocrinology
SN - 0888-8809
IS - 7
ER -