A Reexamination of Thioredoxin Reductase from Thermoplasma acidophilum, a Thermoacidophilic Euryarchaeon, Identifies It as an NADH-Dependent Enzyme

Dwi Susanti; Usha Loganathan; Austin Compton; Biswarup Mukhopadhyay

doi:10.1021/acsomega.7b00640

A Reexamination of Thioredoxin Reductase from Thermoplasma acidophilum, a Thermoacidophilic Euryarchaeon, Identifies It as an NADH-Dependent Enzyme

ACS Omega. 2017 Aug 31;2(8):4180-4187. doi: 10.1021/acsomega.7b00640. Epub 2017 Aug 3.

Authors

Dwi Susanti¹, Usha Loganathan¹, Austin Compton¹, Biswarup Mukhopadhyay¹

Affiliation

¹ Department of Biochemistry, Biocomplexity Institute, and Virginia Tech Carilion School of Medicine, Virginia Tech, Blacksburg, Virginia 24061, United States.

Abstract

Flavin-containing Trx reductase (TrxR) of Thermoplasma acidophilum (Ta), a thermoacidophilic facultative anaerobic archaeon, lacks the structural features for the binding of 2'-phosphate of nicotinamide adenine dinucleotide phosphate (NADPH), and this feature has justified the observed lack of activity with NADPH; NADH has also been reported to be ineffective. Our recent phylogenetic analysis identified Ta-TrxR as closely related to the NADH-dependent enzymes of Thermotoga maritima and Desulfovibrio vulgaris, both being anaerobic bacteria. This observation instigated a reexamination of the activity of the enzyme, which showed that Ta-TrxR is NADH dependent; the apparent K_m for NADH was 3.1 μM, a physiologically relevant value. This finding is consistent with the observation that NADH:TrxR has thus far been found primarily in anaerobic bacteria and archaea.