Beneficial Microbes: Food, Pharma, Aqua & Beverages Industry

Biography

Biography: Maciej Szaleniec

Abstract

Sterolibacterium denitrificans is a denitrifying bacterium that under anaerobic conditions mineralizes cholesterol [1]. It is a source of new region-selective enzymes that can be consider as an interesting biocatalysts for the industry. The initial degradation step of choresterol, ring A oxidation and isomerisation to cholest-4-en-3-one, is catalyzed by cholesterol dehydrogenase/isomerase (AcmA). This product is further oxidized to cholesta-1,4-dien-3-one by cholest-4-en-3-one-∆1-dehydrogenase (AcmB) [2]. Subsequently, both products are hydroxylated at tertiary C25 of the alkyl side chain by steroid C25 dehydrogenase (S25DH) using water as an oxygen donor. S25DH is a heterotrimer (αβγ), containing a molybdopterin guanine dinucleotide cofactor (MGD), 5 FeS clusters and a heme belonging to EBDH-like family [3]. The hydroxylation of cholesterol and its derivatives with S25DH provides an opportunities for application of the enzyme in synthesis of signal compounds and hormones such as 25-hydroxycholesterol and vitamin D3 derivatives. Homogenous and immobilized S25DH was used to convert range of substrates (e.g. cholest-4-en-3-one, cholest-1,4-dien-3-one, cholest-4,6-dien-3-one) under optimized reaction conditions. As the crystal structure of the enzyme is still unknown a homology model of  catalytic subunit S25DH was constructed. MD simulations and docking experiments followed by QM:MM studies provided insight into S25DH catalytic characteristics, which is a first step in understanding of the catalytic mechanism. [1] Dermer, J., and Fuchs, G. J. Biol. Chem.. 2012, 287, 36905–36916 [2] Chiang, et al. J. Bacteriology 2008, 190, 905-914. [3] M. Szaleniec, et. al., Biochemistry 2007, 46 (2007) 7637-7646 Authors acknowledge the financial support from grant projects: LIDER/33/147/L-3/11/NCBR and SONATA 012/05/D/ST4/00277.