Metabolic profiling for the discovery of two rare fusidane-type heterodimers from the fungal endophyte Acremonium pilosum F47.

In our process of studying fusidane-type antibiotics, metabolomics-guided chemical investigation on the endophytic Acremonium pilosum F47 led to the isolation of two unique heterodimers, acremonidiols B and C (1 and 2) consisting of a fusidane-type triterpenoid motif and a steroid unit. Four biosynthetically related known natural products including fusidic acid (FA, 3), as well as ergosterol derivatives (4-6) were also obtained. Their structures were determined by the analyses of ESI-HRMS and NMR data. Compounds 1 and 2, as hybrid molecules comprising the fusidane triterpenoid and steroid, are rare in nature. Compared with the clinically used antibiotic FA (3), new compounds 1 and 2 showed no obvious antibiotic activity, indicating the importance of free C-21 carboxyl group for antibacterial activity.

Old fusidane-type antibiotics for new challenges: Chemistry and biology.

The spread of antibiotic-resistant bacteria and exhausted drug leads render some infections untreatable now and in the future. To deal with these "new challenges", scientists tend to re-pick up "old antibiotics". Fusidane-type antibiotics have been known for nearly 80 years as potent antibacterial agents against gram-positive bacteria, especially Staphylococci, and represent the only triterpene-derived antibiotic class in clinical setting. These attractive characteristics have drawn renewed attention on fusidane-type antibiotics in recent decades. Isolation, characterization, biological evaluation, as well as chemical modifications of fusidane-type antibiotics are increasingly being reported. Combinatorial biosynthesis of this type of antibiotics has been successfully utilized not only for elucidating the biosynthetic pathways, but also for expanding their structural diversity. Some isolated and synthetic compounds exhibit comparable or even more potent biological activity than fusidic acid. This review provides an overview of progress on the studies of structure and biology of fusidane-type antibiotics from 1943 to April 2021. The informative structure-activity relationship is also highlighted.

Old fusidane-type antibiotics for new challenges: Chemistry and biology / 中国天然药物

The spread of antibiotic-resistant bacteria and exhausted drug leads render some infections untreatable now and in the future. To deal with these "new challenges", scientists tend to re-pick up "old antibiotics". Fusidane-type antibiotics have been known for nearly 80 years as potent antibacterial agents against gram-positive bacteria, especially Staphylococci, and represent the only triterpene-derived antibiotic class in clinical setting. These attractive characteristics have drawn renewed attention on fusidane-type antibiotics in recent decades. Isolation, characterization, biological evaluation, as well as chemical modifications of fusidane-type antibiotics are increasingly being reported. Combinatorial biosynthesis of this type of antibiotics has been successfully utilized not only for elucidating the biosynthetic pathways, but also for expanding their structural diversity. Some isolated and synthetic compounds exhibit comparable or even more potent biological activity than fusidic acid. This review provides an overview of progress on the studies of structure and biology of fusidane-type antibiotics from 1943 to April 2021. The informative structure-activity relationship is also highlighted.

Extensive expansion of the chemical diversity of fusidane-type antibiotics using a stochastic combinational strategy.

Fusidane-type antibiotics, represented by helvolic acid, fusidic acid and cephalosporin P1, are fungi-derived antimicrobials with little cross-resistance to commonly used antibiotics. Generation of new fusidane-type derivatives is therefore of great value, but this is hindered by available approaches. Here, we developed a stochastic combinational strategy by random assembly of all the post-tailoring genes derived from helvolic acid, fusidic acid, and cephalosporin P1 biosynthetic pathways in a strain that produces their common intermediate. Among a total of 27 gene combinations, 24 combinations produce expected products and afford 58 fusidane-type analogues, of which 54 are new compounds. Moreover, random gene combination can induce unexpected activity of some post-tailoring enzymes, leading to a further increase in chemical diversity. These newly generated derivatives provide new insights into the structure‒activity relationship of fusidane-type antibiotics. The stochastic combinational strategy established in this study proves to be a powerful approach for expanding structural diversity of natural products.

Extensive expansion of the chemical diversity of fusidane-type antibiotics using a stochastic combinational strategy

Fusidane-type antibiotics, represented by helvolic acid, fusidic acid and cephalosporin P

Origin and Evolution of Fusidane-Type Antibiotics Biosynthetic Pathway through Multiple Horizontal Gene Transfers.

Fusidane-type antibiotics represented by fusidic acid, helvolic acid, and cephalosporin P1 have very similar core structures, but they are produced by fungi belonging to different taxonomic groups. The origin and evolution of fusidane-type antibiotics biosynthetic gene clusters (BGCs) in different antibiotics producing strains remained an enigma. In this study, we investigated the distribution and evolution of the fusidane BGCs in 1,284 fungal genomes. We identified 12 helvolic acid BGCs, 4 fusidic acid BGCs, and 1 cephalosporin P1 BGC in Pezizomycotina fungi. Phylogenetic analyses indicated six horizontal gene transfer (HGT) events in the evolutionary trajectory of the BGCs, including 1) three transfers across Eurotiomycetes and Sordariomycetes classes; 2) one transfer between genera under Sordariomycetes class; and 3) two transfers within Aspergillus genus under Eurotiomycetes classes. Finally, we proposed that the ancestor of fusidane BGCs would be originated from the Zoopagomycota by ancient HGT events according to the phylogenetic trees of key enzymes in fusidane BGCs (OSC and P450 genes). Our results extensively clarify the evolutionary trajectory of fusidane BGCs by HGT among distantly related fungi and provide new insights into the evolutionary mechanisms of metabolic pathways in fungi.

Biosynthesis of clinically used antibiotic fusidic acid and identification of two short-chain dehydrogenase/reductases with converse stereoselectivity.

Fusidic acid is the only fusidane-type antibiotic that has been clinically used. However, biosynthesis of this important molecule in fungi is poorly understood. We have recently elucidated the biosynthesis of fusidane-type antibiotic helvolic acid, which provides us with clues to identify a possible gene cluster for fusidic acid (fus cluster). This gene cluster consists of eight genes, among which six are conserved in the helvolic acid gene cluster except fusC1 and fusB1. Introduction of the two genes into the Aspergillus oryzae NSAR1 expressing the conserved six genes led to the production of fusidic acid. A stepwise introduction of fusC1 and fusB1 revealed that the two genes worked independently without a strict reaction order. Notably, we identified two short-chain dehydrogenase/reductase genes fusC1 and fusC2 in the fus cluster, which showed converse stereoselectivity in 3-ketoreduction. This is the first report on the biosynthesis and heterologous expression of fusidic acid.

Biosynthesis of clinically used antibiotic fusidic acid and identification of two short-chain dehydrogenase/reductases with converse stereoselectivity

Fusidic acid is the only fusidane-type antibiotic that has been clinically used. However, biosynthesis of this important molecule in fungi is poorly understood. We have recently elucidated the biosynthesis of fusidane-type antibiotic helvolic acid, which provides us with clues to identify a possible gene cluster for fusidic acid ( cluster). This gene cluster consists of eight genes, among which six are conserved in the helvolic acid gene cluster except and . Introduction of the two genes into the NSAR1 expressing the conserved six genes led to the production of fusidic acid. A stepwise introduction of and revealed that the two genes worked independently without a strict reaction order. Notably, we identified two short-chain dehydrogenase/reductase genes and in the cluster, which showed converse stereoselectivity in 3-ketoreduction. This is the first report on the biosynthesis and heterologous expression of fusidic acid.