Redirecting P450 EryK Specificity by Rational Site-Directed Mutagenesis

Substrate-induced conformational change in cytochrome P450 OleP

The regulation of cytochrome P450 activity is often achieved by structural transitions induced by substrate binding. We describe the conformational transition experienced upon binding by the P450 OleP, an epoxygenase involved in oleandomycin biosynthesis. OleP bound to the substrate analog 6DEB crystallized in 2 forms: one with an ensemble of open and closed conformations in the asymmetric unit and another with only the closed conformation. Characterization of OleP-6DEB binding kinetics, also using the P450 inhibitor clotrimazole, unveiled a complex binding mechanism that involves slow conformational rearrangement with the accumulation of a spectroscopically detectable intermediate where 6DEB is bound to open OleP. Data reported herein provide structural snapshots of key precatalytic steps in the OleP reaction and explain how structural rearrangements induced by substrate binding regulate activity.-Parisi, G., Montemiglio, L. C., Giuffrè, A., Macone, A., Scaglione, A., Cerutti, G., Exertier, C., Savino, C., Vallone, B. Substrate-induced conformational change in cytochrome P450 OleP.

Molecular characterization of the hydroxylase HmtN at 1.3 Å resolution

Himastatin is a novel antibiotic with antitumor and antibacterial activity. In the himastatin biosynthesis pathway, HmtN is responsible for the hydroxylation of the piperazic acid (Pip) motif. Herein, we present the crystal structures of HmtN (1.3 Å), which is the first structure for a cytochrome P450 involved in the hydroxylation of cyclohexadepsipeptide during himastatin biosynthesis. Structure analysis indicated that almost all the surface of HmtN has negative electrostatic potential, only small patches of positive electrostatic potential can be found. It is worth noting that almost the entire active site of HmtT is negatively charged, while HmtN active site is composed of positive and negative charge. This may be relevant to their specific substrate recognition and different catalytic function. In addition, three channels were observed in HmtN crystal structure; channel 3 may be essential for substrate ingress and egress from the active site to the surface, while channel 1 and channel 2 may be the solvent and water pathway, respectively.

Engineering of global regulator cAMP receptor protein (CRP) in Escherichia coli for improved lycopene production

Transcriptional engineering has received significant attention for improving strains by modulating the behavior of transcription factors, which could be used to reprogram a series of gene transcriptions and enable multiple simultaneous modifications at the genomic level. In this study, engineering of the cAMP receptor protein (CRP) was explored with the aim of subtly balancing entire pathway networks and potentially improving lycopene production without significant genetic intervention in other pathways. Amino acid mutations were introduced to CRP by error-prone PCR, and three variants (mcrp26, mcrp159 and mcrp424) with increased lycopene productivity were screened. Combinations of three point mutations were then created via site-directed mutagenesis. The best mutant gene (mcrp26) was integrated into the genome of E. coli BW25113-BIE to replace the wild-type crp gene (MT-1), which resulted in a higher lycopene production (18.49mg/g DCW) compared to the original strain (WT). The mutant strain MT-1 was further investigated in a 10-L bench-top fermentor with a lycopene yield of 128mg/l at 20h, approximately 25% higher than WT. DNA microarray analyses showed that 396 genes (229 up-regulated and 167 down-regulated) were differentially expressed in the mutant MT-1 compared to WT. Finally, the introduction of the mutant crp gene (mcrp26) increased β-carotene production in E. coli. This is the first report of improving the phenotype for metabolite overproduction in E. coli using a CRP engineering strategy.