Charged Amino Acids in the Transmembrane Helix Strongly Affect the Enzyme Activity of Aromatase

Abstract

Estrogens play critical roles in embryonic development, gonadal sex differentiation, behavior, and reproduction in vertebrates and in several human cancers. Estrogens are synthesized from testosterone and androstenedione by the endoplasmic reticulum membrane-bound P450 aromatase/cytochrome P450 oxidoreductase complex (CYP19/CPR). Here, we report the characterization of novel mammalian CYP19 isoforms encoded by CYP19 gene copies. These CYP19 isoforms are all defined by a combination of mutations in the N-terminal transmembrane helix (E42K, D43N) and in helix C of the catalytic domain (P146T, F147Y). The mutant CYP19 isoforms show increased androgen conversion due to the KN transmembrane helix. In addition, the TY substitutions in helix C result in a substrate preference for androstenedione. Our structural models suggest that CYP19 mutants may interact differently with the membrane (affecting substrate uptake) and with CPR (affecting electron transfer), providing structural clues for the catalytic differences.

Expression of GLOD4 Gene in the Testis of Qianbei Ma Goats and Its Effect on Testicular Leydig Cells

“…In turn, STAR catalyzes the substrate of the cytochrome P450 cholesterol side chain cleavage enzyme (CYP11A1) reaction and converts it to pregnenolone, which is then catalyzed to progesterone by the micronutrient enzyme 3B-hydroxysteroid dehydrogenase 1 (3β-HSD1) in the smooth endoplasmic reticulum [41]. Progesterone is ultimately converted to testosterone by a series of steroid synthases [42][43][44]. These functional genes play a critical role in regulating testosterone secretion.…”