A division of labor between two biotin protein ligase homologs

Advances in biotin biosynthesis and biotechnological production in microorganisms

Biotin, also known as vitamin H or B7, acts as a crucial cofactor in the central metabolism processes of fatty acids, amino acids, and carbohydrates. Biotin has important applications in food additives, biomedicine, and other fields. While the ability to synthesize biotin de novo is confined to microorganisms and plants, humans and animals require substantial daily intake, primarily through dietary sources and intestinal microflora. Currently, chemical synthesis stands as the primary method for commercial biotin production, although microbial biotin production offers an environmentally sustainable alternative with promising prospects. This review presents a comprehensive overview of the pathways involved in de novo biotin synthesis in various species of microbes and insights into its regulatory and transport systems. Furthermore, diverse strategies are discussed to improve the biotin production here, including mutation breeding, rational metabolic engineering design, artificial genetic modification, and process optimization. The review also presents the potential strategies for addressing current challenges for industrial-scale bioproduction of biotin in the future. This review is very helpful for exploring efficient and sustainable strategies for large-scale biotin production.

Biotin protein ligase as you like it: Either extraordinarily specific or promiscuous protein biotinylation

Biotin (vitamin H or B7) is a coenzyme essential for all forms of life. Biotin has biological activity only when covalently attached to a few key metabolic enzyme proteins. Most organisms have only one attachment enzyme, biotin protein ligase (BPL), which attaches biotin to all target proteins. The sequences of these proteins and their substrate proteins are strongly conserved throughout biology. Structures of both the biotin ligase- and biotin-acceptor domains of mammals, plants, several bacterial species, and archaea have been determined. These, together with mutational analyses of ligases and their protein substrates, illustrate the exceptional specificity of this protein modification. For example, the Escherichia coli BPL biotinylates only one of the >4000 cellular proteins. Several bifunctional bacterial biotin ligases transcriptionally regulate biotin synthesis and/or transport in concert with biotinylation. The human BPL has been demonstrated to play an important role in that mutations in the BPL encoding gene cause one form of the disease, biotin-responsive multiple carboxylase deficiency. Promiscuous mutant versions of several BPL enzymes release biotinoyl-AMP, the active intermediate of the ligase reaction, to solvent. The released biotinoyl-AMP acts as a chemical biotinylation reagent that modifies lysine residues of neighboring proteins in vivo. This proximity-dependent biotinylation (called BioID) approach has been heavily utilized in cell biology.

A conserved and seemingly redundant Escherichia coli biotin biosynthesis gene expressed only during anaerobic growth

Biotin is an essential metabolic cofactor and de novo biotin biosynthetic pathways are widespread in microorganisms and plants. Biotin synthetic genes are generally found clustered into bio operons to facilitate tight regulation since biotin synthesis is a metabolically expensive process. Dethiobiotin synthetase (DTBS) catalyzes the penultimate step of biotin biosynthesis, the formation of 7,8-diaminononanoate (DAPA). In Escherichia coli, DTBS is encoded by the bio operon gene bioD. Several studies have reported transcriptional activation of ynfK a gene of unknown function, under anaerobic conditions. Alignments of YnfK with BioD have led to suggestions that YnfK has DTBS activity. We report that YnfK is a functional DTBS, although an enzyme of poor activity that is poorly expressed. Supplementation of growth medium with DAPA or substitution of BioD active site residues for the corresponding YnfK residues greatly improved the DTBS activity of YnfK. We confirmed that FNR activates transcriptional level of ynfK during anaerobic growth and identified the FNR binding site of ynfK. The ynfK gene is well conserved in γ-proteobacteria.