Progress of 3-ketosteroid Δ 1 -dehydrogenases for steroid production

3-ketosteroid Δ 1 -dehydrogenases (Δ 1 -KstDs) are FAD-dependent and substrate-inducing enzymes, which catalyze the introduction of double bonds between C1 and C2 atoms of the A ring of 3-ketosteroid substrates. They are essential in the initial stages of the steroid core's breakdown. Additionally, Δ 1 -KstDs are particularly intriguing for applications in pharmaceutical manufacturing, environmental bioremediation, and the etiology of infectious illnesses. A wide range of microorganisms, particularly bacteria from the phylum Actinobacteria, have Δ 1 -KstDs. Δ 1 -KstDs can be classified into at least seven separate groups based on the sequence data in NCBI, and the enzymes in each group exhibit unique structural and catalytic properties. Understanding these properties completely is crucial for utilizing and developing Δ 1 -KstDs in metabolic engineering and enzyme engineering. This review describes and explains the biochemical and enzymatic characteristics of Δ 1 -KstDs based on a phylogenetic tree. To assist in the selection of highly active enzymes for engineering applications, the three-dimensional structures of Δ 1 -KstDs associated with enzyme mechanisms are stressed. The biotechnological application of microbial Δ 1 -KstDs is also covered in this article, including genetic engineering based on metabolic strains and related genetic modification techniques for creating new productive industrial strains, the development and transformation of the heterologous expression system, the molecular modification and the optimization of catalytic conditions, and the use of microbial fermentation to increase product yield. Furthermore, we also highlight the recent development in the use of isolated Δ 1 -KstDs combined with a FAD cofactor regeneration system. We conclude by summarizing the concepts and techniques used in subsequent research and application development. All of these knowledge might serve as a guide for new mining and industrial applications in Δ 1 -KstDs.