Bacterial Biosynthetic P450 Enzyme PikCD50N: A Potential Biocatalyst for the Preparation of Human Drug Metabolites

Genetic Code Expansion: Recent Developments and Emerging Applications

The concept of genetic code expansion (GCE) has revolutionized the field of chemical and synthetic biology, enabling the site-specific incorporation of noncanonical amino acids (ncAAs) into proteins, thus opening new avenues in research and applications across biology and medicine. In this review, we cover the principles of GCE, including the optimization of the aminoacyl-tRNA synthetase (aaRS)/tRNA system and the advancements in translation system engineering. Notable developments include the refinement of aaRS/tRNA pairs, enhancements in screening methods, and the biosynthesis of noncanonical amino acids. The applications of GCE technology span from synthetic biology, where it facilitates gene expression regulation and protein engineering, to medicine, with promising approaches in drug development, vaccine production, and gene editing. The review concludes with a perspective on the future of GCE, underscoring its potential to further expand the toolkit of biology and medicine. Through this comprehensive review, we aim to provide a detailed overview of the current state of GCE technology, its challenges, opportunities, and the frontier it represents in the expansion of the genetic code for novel biological research and therapeutic applications.

Semiconductor Effect from Pd(II) Porphyrin Metal to Its Ligand in Photocatalytic N-Dealkylation

In this work, four saddled Pd(II) porphyrins were developed as photocatalyst for N-dealkylation of triethyl Rhodamine (TER) under visible light, and their catalytic ability was found to be negatively related to the out-of-plane of their macrocycles. Two important relationships involving the metalloporphyrins as catalyst were revealed: (1) a photoexcitative semiconductor effect between the 4dx 2-γ 2(Pd) and a2u(π) orbitals of Pd(II) porphyrin on the dealkylation. (2) a domino process from strap length, ring geometry, core deformation, d-π gap variation, to photocatalytic activity. Two revelations imply a unidirectional electron transfer route from axial ligand, to central metal, to porphyrin ring based on photoexcitation and guide the design and development of complex photocatalysts, and their revelation is attributed to the acquisition of a series of Pd(II) porphyrins with continuous ring distortion. The findings help to understand the photocatalytic single electron transfer (SET)-first mechanism based on metallic complex.

Discovery and biosynthesis of bacterial drimane-type sesquiterpenoids from Streptomyces clavuligerus

Drimane-type sesquiterpenoids (DMTs) are characterized by a distinctive 6/6 bicyclic skeleton comprising the A and B rings. While DMTs are commonly found in fungi and plants, their presence in bacteria has not been reported. Moreover, the biosynthetic pathways for DMTs have been primarily elucidated in fungi, with identified P450s only acting on the B ring. In this study, we isolated and characterized three bacterial DMTs, namely 3β-hydroxydrimenol (2), 2α-hydroxydrimenol (3), and 3-ketodrimenol (4), from Streptomyces clavuligerus. Through genome mining and heterologous expression, we identified a cav biosynthetic gene cluster responsible for the biosynthesis of DMTs 2-4, along with a P450, CavA, responsible for introducing the C-2 and C-3 hydroxy groups. Furthermore, the substrate scope of CavA revealed its ability to hydroxylate drimenol analogs. This discovery not only broadens the known chemical diversity of DMTs from bacteria, but also provides new insights into DMT biosynthesis in bacteria.

Production of hybrid macrolide antibiotics by exploiting the specific substrate recognition characteristics of multifunctional cytochrome P450 enzyme MycG

Macrolide antibiotics are biosynthesized via enzymatic modifications, including glycosylation, methylation, and oxidation, after the core macro-lactone ring is generated by a polyketide synthase system. This study explored the diversification of macrolides by combining biosynthetic enzymes and reports an approach to produce unnatural hybrid macrolide antibiotics. The cytochrome (CYP) P450 monooxygenase MycG exhibits bifunctional activity, catalyzing late-stage hydroxylation at C-14 followed by epoxidation at C-12/13 during mycinamicin biosynthesis. The mycinose sugar of mycinamicin serves as a key molecular recognition element for binding to MycG. Thus, we subjected the hybrid macrolide antibiotic 23-O-mycinosyl-20-deoxo-20-dihydro-12,13-deepoxyrosamicin (IZI) to MycG, and confirmed that MycG catalyzed hydroxylation at C-22 and epoxidation at C-12/13 in IZI. In addition, the introduction of mycinose biosynthesis-related genes and mycG into rosamicin-producing Micromonospora rosaria enabled the fermentative production of 22-hydroxylated and 12,13-epoxidized forms of IZI. Interestingly, MycG catalyzed the sequential oxidation of hydroxylation and epoxidation in mycinamicin biosynthesis, but only single reactions in IZI. These findings highlight the potential for expanding the application of the multifunctional P450 monooxygenase MycG for the production of unnatural compounds.

Unnatural activities and mechanistic insights of cytochrome P450 PikC gained from site-specific mutagenesis by non-canonical amino acids

Cytochrome P450 enzymes play important roles in the biosynthesis of macrolide antibiotics by mediating a vast variety of regio- and stereoselective oxidative modifications, thus improving their chemical diversity, biological activities, and pharmaceutical properties. Tremendous efforts have been made on engineering the reactivity and selectivity of these useful biocatalysts. However, the 20 proteinogenic amino acids cannot always satisfy the requirement of site-directed/random mutagenesis and rational protein design of P450 enzymes. To address this issue, herein, we practice the semi-rational non-canonical amino acid mutagenesis for the pikromycin biosynthetic P450 enzyme PikC, which recognizes its native macrolide substrates with a 12- or 14-membered ring macrolactone linked to a deoxyamino sugar through a unique sugar-anchoring mechanism. Based on a semi-rationally designed substrate binding strategy, non-canonical amino acid mutagenesis at the His238 position enables the unnatural activities of several PikC mutants towards the macrolactone precursors without any sugar appendix. With the aglycone hydroxylating activities, the pikromycin biosynthetic pathway is rewired by the representative mutant PikC_H238pAcF carrying a p-acetylphenylalanine residue at the His238 position and a promiscuous glycosyltransferase. Moreover, structural analysis of substrate-free and three different enzyme-substrate complexes of PikC_H238pAcF provides significant mechanistic insights into the substrate binding and catalytic selectivity of this paradigm biosynthetic P450 enzyme.

Functional expression and purification of DoxA, a key cytochrome P450 from Streptomyces peucetius ATCC 27952

The antitumor drug doxorubicin is widely used in clinical practice. However, the low yield and high cost of this drug highlight the urgent need for cost-effective processes to rapidly manufacture antitumor drugs at scale. In the biosynthesis pathway, the multi-functional cytochrome P450 enzyme DoxA catalyzes the last three steps of hydroxylation. The final conversion of daunorubicin to doxorubicin is the rate-limiting step. In our work, the DoxA has been expressed with the ferredoxin reductase FDR2 and the ferredoxin FDX1 and purified to homogeneous. The reduced carbon monoxide difference spectroscopy, heme concentration, and enzymatic characteristic were characterized. These studies suggest an approach for engineering Streptomyces P450s with functional expression for mechanistic and structural studies.