3CTY

Crystal structure of T. acidophilum thioredoxin reductase

Summary for 3CTY

• Entry DOI: 10.2210/pdb3cty/pdb
• Descriptor: Thioredoxin reductase, FLAVIN-ADENINE DINUCLEOTIDE (3 entities in total)
• Functional Keywords: thioredoxin reductase, fad, oxidoreductase, flavin, flavoprotein
• Biological source: Thermoplasma acidophilum
• Total number of polymer chains: 2
• Total formula weight: 70148.69

Authors

Hernandez, H.H.,Drennan, C.L. (deposition date: 2008-04-14, release date: 2009-02-24, Last modification date: 2017-10-25)

Primary citation

Hernandez, H.H.,Jaquez, O.A.,Hamill, M.J.,Elliott, S.J.,Drennan, C.L.
Thioredoxin reductase from Thermoplasma acidophilum: a new twist on redox regulation.
Biochemistry, 47:9728-9737, 2008

PubMed Abstract: Thioredoxin reductases (TrxRs) regulate the intracellular redox environment by using NADPH to provide reducing equivalents for thioredoxins (Trxs). Here we present the cloning and biochemical characterization of a putative TrxR (Ta0984) and a putative Trx (Ta0866) from Thermoplasma acidophilum. Our data identify Ta0866 as a Trx through its capacity to reduce insulin and be reduced by Escherichia coli TrxR in a NADPH-dependent manner. Our data also establish Ta0984 as a TrxR due to its ability to reduce T. acidophilum Trx ( taTrx), although not in a NADPH- or NADH-dependent manner. To explore the apparent inability of taTrxR to use NADPH or NADH as a reductant, we carried out a complete electrochemical characterization, which suggests that redox potential is not the source of this nonreactivity [Hamill et al. (2008) Biochemistry 47, 9738-9746]. Turning to crystallographic analysis, a 2.35 A resolution structure of taTrxR, also presented here, shows that despite the overall structural similarity to the well-characterized TrxR from E. coli (RMSD 1.30 A (2) for chain A), the "NADPH binding pocket" is not conserved. E. coli TrxR residues implicated in NADPH binding, H175, R176, R177, and R181, have been substituted with E185, Y186, M187, and M191 in the ta protein. Thus, we have identified a Trx and TrxR protein system from T. acidophilum for which the TrxR shares overall structural and redox properties with other TrxRs but lacks the appropriate binding motif to use the standard NADPH reductant. Our discovery of a TrxR that does not use NADPH provides a new twist in redox regulation.

PubMed: 18717593
DOI: 10.1021/bi8006753

Experimental method

X-RAY DIFFRACTION (2.35 Å)