Differential interaction of erythromycin with cytochromes P450 3A1/2 in the endoplasmic reticulum: a CO flash photolysis study

Surface hydrophobics mediate functional dimerization of CYP121A1 of Mycobacterium tuberculosis

Tuberculosis is caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb) and remains the leading cause of death by infection world-wide. The Mtb genome encodes a disproportionate number of twenty cytochrome P450 enzymes, of which the essential enzyme cytochrome P450 121A1 (CYP121A1) remains a target of drug design efforts. CYP121A1 mediates a phenol coupling reaction of the tyrosine dipeptide cyclo-L-Tyr-L-Tyr (cYY). In this work, a structure and function investigation of dimerization was performed as an overlooked feature of CYP121A1 function. This investigation showed that CYP121A1 dimers form via intermolecular contacts on the distal surface and are mediated by a network of solvent-exposed hydrophobic residues. Disruption of CYP121A1 dimers by site-directed mutagenesis leads to a partial loss of specificity for cYY, resulting in an approximate 75% decrease in catalysis. ¹⁹F labeling and nuclear magnetic resonance of the enzyme FG-loop was also combined with protein docking to develop a working model of a functional CYP121A1 dimer. The results obtained suggest that participation of a homodimer interface in substrate selectivity represents a novel paradigm of substrate binding in CYPs, while also providing important mechanistic insight regarding a relevant drug target in the development of novel anti-tuberculosis agents.

Physical Studies of P450-P450 Interactions: Predicting Quaternary Structures of P450 Complexes in Membranes from Their X-ray Crystal Structures

Cytochrome P450 enzymes, which catalyze oxygenation reactions of both exogenous and endogenous chemicals, are membrane bound proteins that require interaction with their redox partners in order to function. Those responsible for drug and foreign compound metabolism are localized primarily in the endoplasmic reticulum of liver, lung, intestine, and other tissues. More recently, the potential for P450 enzymes to exist as supramolecular complexes has been shown by the demonstration of both homomeric and heteromeric complexes. The P450 units in these complexes are heterogeneous with respect to their distribution and function, and the interaction of different P450s can influence P450-specific metabolism. The goal of this review is to examine the evidence supporting the existence of physical complexes among P450 enzymes. Additionally, the review examines the crystal lattices of different P450 enzymes derived from X-ray diffraction data to make assumptions regarding possible quaternary structures in membranes and in turn, to predict how the quaternary structures could influence metabolism and explain the functional effects of specific P450-P450 interactions.

Mechanism of interactions of alpha-naphthoflavone with cytochrome P450 3A4 explored with an engineered enzyme bearing a fluorescent probe

Design of a partially cysteine-depleted C98S/C239S/C377S/C468A cytochrome P450 3A4 mutant designated CYP3A4(C58,C64) allowed site-directed incorporation of thiol-reactive fluorescent probes into alpha-helix A. The site of modification was identified as Cys-64 with the help of CYP3A4(C58) and CYP3A4(C64), each bearing only one accessible cysteine. Changes in the fluorescence of CYP3A4(C58,C64) labeled with 6-(bromoacetyl)-2-(dimethylamino)naphthalene (BADAN), 7-(diethylamino)-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM), or monobromobimane (mBBr) were used to study the interactions with bromocriptine (BCT), 1-pyrenebutanol (1-PB), testosterone (TST), and alpha-naphthoflavone (ANF). Of these substrates only ANF has a specific effect, causing a considerable decrease in fluorescence intensity of BADAN and CPM and increasing the fluorescence of mBBr. This ANF-binding event in the case of the BADAN-modified enzyme is characterized by an S50 of 18.2 +/- 0.7, compared with the value of 2.2 +/- 0.3 for the ANF-induced spin transition, thus revealing an additional low-affinity binding site. Studies of the effect of TST, 1-PB, and BCT on the interactions of ANF monitored by changes in fluorescence of CYP3A4(C58,C64)-BADAN or by the ANF-induced spin transition revealed no competition by these substrates. Investigation of the kinetics of fluorescence increase upon H2O2-dependent heme depletion suggests that labeled CYP3A4(C58,C64) is represented by two conformers, one of which has the fluorescence of the BADAN and CPM labels completely quenched, presumably by photoinduced electron transfer from the neighboring Trp-72 and/or Tyr-68 residues. The binding of ANF to the newly discovered binding site appears to affect the interactions of the label with the above residue(s), thus modulating the fraction of the fluorescent conformer.