Thioredoxin Reductase From Thermoplasma Acidophilum: a New Twist on Redox Regulation

Journal Article · Mon May 18 04:00:00 EDT 2009 · Biochem. 47:9728,2008

OSTI ID:953120

Hernandez, H H; Jaquez, O A; Hamill, M J; Elliott, S J; Drennan, C L

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 {angstrom} 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 {angstrom}{sup 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.

• Research Organization: Stanford Linear Accelerator Center (SLAC)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 953120
• Report Number(s): SLAC-REPRINT-2009-164
• Journal Information: Biochem. 47:9728,2008, Journal Name: Biochem. 47:9728,2008 Journal Issue: 37 Vol. 47
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
BIOCHEMISTRY
CAPACITY
CHAINS
CLONING
ESCHERICHIA COLI
INSULIN
OXIDOREDUCTASES
Other
BIO
CHEM
PROTEINS
REDOX POTENTIAL
REGULATIONS
RESIDUES
RESOLUTION