Optimization of hydrogenobyrinic acid biosynthesis in Escherichia coli using multi-level metabolic engineering strategies

Multi-modular metabolic engineering of heme synthesis in Corynebacterium glutamicum

Heme, an iron-containing porphyrin derivative, holds great promise in fields like medicine, food production and chemicals. Here, we developed an engineered Corynebacterium glutamicum strain for efficient heme production by combining modular engineering and RBS engineering. The whole heme biosynthetic pathway was methodically divided into 5-ALA synthetic module, uroporphyrinogen III (UPG III) synthetic module and heme synthetic module for further construction and optimization. Three heme synthetic modules were compared and the siroheme-dependent (SHD) pathway was identified to be optimal in C. glutamicum for the first time. To further improve heme production, the expression of genes in UPG III synthetic module and heme synthetic module was coordinated optimized through RBS engineering, respectively. Subsequently, heme oxygenase was knocked out to reduce heme degradation. The engineered strain HS12 showed a maximum iron-containing porphyrin derivatives titer of 1592 mg/L with the extracellular secretion rate of 45.5% in fed-batch fermentation. Our study constructed a C. glutamicum chassis strain for efficient heme accumulation, which was beneficial for the advancement of efficient heme and other porphyrins production.

A comprehensive review on the recent advances for 5-aminolevulinic acid production by the engineered bacteria

5-Aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid essential for synthesizing tetrapyrrole compounds, including heme, chlorophyll, cytochrome, and vitamin B12. As a plant growth regulator, 5-ALA is extensively used in agriculture to enhance crop yield and quality. The complexity and low yield of chemical synthesis methods have led to significant interest in the microbial synthesis of 5-ALA. Advanced strategies, including the: enhancement of precursor and cofactor supply, compartmentalization of key enzymes, product transporters engineering, by-product formation reduction, and biosensor-based dynamic regulation, have been implemented in bacteria for 5-ALA production, significantly advancing its industrialization. This article offers a comprehensive review of recent developments in 5-ALA production using engineered bacteria and presents new insights to propel the field forward.

Optimization of Hydrogenobyrinic Acid Synthesis in a Cell-Free Multienzyme Reaction by Novel S-Adenosyl-methionine Regeneration

Hydrogenobyrinic acid, a modified tetrapyrrole composed of eight five-carbon compounds, is a key intermediate and central framework of vitamin B₁₂. Synthesis of hydrogenobyrinic acid requires eight S-adenosyl-methionine working as the methyl group donor catalyzed by 12 enzymes including six methyltransferases, causing the great shortage of S-adenosyl-methionine and accumulation of S-adenosyl-homocysteine, which is uneconomic and unsustainable for the cascade reaction. Here, we report a cell-free synthetic system for producing hydrogenobyrinic acid by integrating 12 enzymes using 5-aminolevulininate as a substrate and develop a novel S-adenosyl-methionine regeneration system to steadily supply S-adenosyl-methionine and avoid the accumulated inhibition of S-adenosyl-homocysteine by consuming a cheaper substrate (l-methionine and polyphosphate). By combination of the reaction system optimization and S-adenosyl-methionine regeneration, the titer of hydrogenobyrinic acid was improved from 0.61 to 29.39 mg/L in a 12 h reaction period, representing an increase of 48.18-fold, raising an efficient and rapidly evolutional alternative method to produce high-value-added compounds and intermediate products.

Methylations in vitamin B12 biosynthesis and catalysis

Vitamin B₁₂ is an essential biomolecule that assists in the catalysis of methyl transfer and radical-based reactions in cellular metabolism. The structure of B₁₂ is characterized by a tetrapyrrolic corrin ring with a central cobalt ion coordinated with an upper ligand, and a lower ligand anchored via a nucleotide loop. Multiple methyl groups decorate B₁₂, and their presence (or absence) have structural and functional consequences. In this minireview, we focus on the methyl groups that distinguish vitamin B₁₂ from other tetrapyrrolic biomolecules and from its own naturally occurring analogues called cobamides. We draw information from recent advances in the field to understand the origins of these methyl groups and the enzymes that incorporate them, and discuss their biological significance.

Recent advances in microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway

Tetrapyrroles are essential metabolic components produced by almost all organisms, and they participate in various fundamental biological processes. Tetrapyrroles are used as pharmaceuticals, food additives, and nutraceuticals, as well as in agricultural applications. However, their production is limited by their low extraction yields from natural resources and by the complex reaction steps involved in their chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, microbial cell factories were developed as an alternative method for tetrapyrrole production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value compounds in the tetrapyrrole biosynthesis pathway (e.g., 5-aminolevulinic acid, heme, bilins, chlorophyll, and vitamin B₁₂). Furthermore, outstanding challenges to the microbial production of tetrapyrrole compounds, as well as their possible solutions, are discussed.

Combinatorial metabolic pathway assembly approaches and toolkits for modular assembly

Synthetic Biology is a rapidly growing interdisciplinary field that is primarily built upon foundational advances in molecular biology combined with engineering design principles such as modularity and interoperability. The field considers living systems as programmable at the genetic level and has been defined by the development of new platform technologies and methodological advances. A key concept driving the field is the Design-Build-Test-Learn cycle which provides a systematic framework for building new biological systems. One major application area for synthetic biology is biosynthetic pathway engineering that requires the modular assembly of different genetic regulatory elements and biosynthetic enzymes. In this review we provide an overview of modular DNA assembly and describe and compare the plethora of in vitro and in vivo assembly methods for combinatorial pathway engineering. Considerations for part design and methods for enzyme balancing are also presented, and we briefly discuss alternatives to intracellular pathway assembly including microbial consortia and cell-free systems for biosynthesis. Finally, we describe computational tools and automation for pathway design and assembly and argue that a deeper understanding of the many different variables of genetic design, pathway regulation and cellular metabolism will allow more predictive pathway design and engineering.