IDENTIFICATION OF A MEANDER REGION PROLINE RESIDUE CRITICAL FOR HEME-BINDING TO CYTOCHROME-P450 - IMPLICATIONS FOR THE CATALYTIC FUNCTION OF HUMAN CYP4B1
Ym. Zheng et al., IDENTIFICATION OF A MEANDER REGION PROLINE RESIDUE CRITICAL FOR HEME-BINDING TO CYTOCHROME-P450 - IMPLICATIONS FOR THE CATALYTIC FUNCTION OF HUMAN CYP4B1, Biochemistry (Easton), 37(37), 1998, pp. 12847-12851
Alignment of xenobiotic-metabolizing P450 protein sequences highlights
an invariant proline residue in the meander region two amino acids N-
terminal to the distal arginine of the putative ERR triad thought to b
e important for heme binding. This occurs as a serine in the sequences
derived from human CYP4B1 gDNA and both human lung and placental CYP4
B1 cDNAs. Reversion of this serine to the conserved proline residue (S
er427 --> Pro) by site-directed mutagenesis conferred the ability to i
ncorporate heme on the human placental enzyme. Mutation of the corresp
onding proline in rabbit CYP4B1 (Pro422 --> Ser) abolished heme incorp
oration. Membrane preparations of human CYP4B1(Pro) and rabbit CYP4B1(
Pro), but not the corresponding CYP4B1(Ser) variants, supported lauric
acid hydroxylation preferentially at the omega-position. Purified, re
constituted human CYP4B1(Pro) and rabbit CYP4B1(Pro) formed 12-hydroxy
lauric acid at rates of 17-21 min(-1), and both enzymes were also C-8
to C-10 fatty acid omega-hydroxylases preferentially, with total rates
of hydroxylation decreasing in the order C-12 > C-10 > C-9 > C-8. Fin
ally, neither human nor rabbit CYP4B1(Pro) formed detectable levels of
any hydroxylated testosterone metabolites. Therefore, the presence of
a consensus Pro-X-Arg motif is critical for incorporation of the heme
prosthetic group in human and rabbit CYP4B1 proteins expressed in ins
ect cells. Native human CYP4B1, expressed in vivo, is likely to be fun
ctionally impaired if Pro427 is required for holoenzyme expression in
mammalian cells.