The negative transcriptional regulator NmrA discriminates between oxidized and reduced dinucleotides.
NmrA, a transcription repressor involved in the regulation of nitrogen metabolism in Aspergillus nidulans,is a member of the short-chain dehydrogenase reductase superfamily. Isothermal titration calorimetry and differential scanning calorimetry have been used to show NmrA binds NAD+ and NADP+ with similar affinity (average KD 65 microM) but has a greatly reduced affinity for NADH and NADPH (average KD 6.0 mM). The structure of NmrA in a complex with NADP+ reveals how repositioning a His-37 side chain allows the different conformations of NAD+ and NADP+ to be accommodated. Modeling NAD(P)H into NmrA indicated that steric clashes, attenuation of electrostatic interactions, and loss of aromatic ring stacking can explain the differing affinities of NAD(P)+/NAD(P)H. The ability of NmrA to discriminate between the oxidized and reduced forms of the dinucleotides may be linked to a possible role in redox sensing. Isothermal titration calorimetry demonstrated that NmrA and a C-terminal fragment of the GATA transcription factor AreA interacted with a 1:1 stoichiometry and an apparent KD of 0.26 microM. NmrA was unable to bind the nitrogen metabolite repression signaling molecules ammonium or glutamine.
Lamb
Heather K
HK
School of Cell and Molecular Biosciences, Catherine Cookson Building, University of Newcastle upon Tyne, Framlington Place, NE2 4HH, United Kingdom.
Leslie
Kris
K
Dodds
Anna L
AL
Nutley
Margaret
M
Cooper
Alan
A
Johnson
Christopher
C
Thompson
Paul
P
Stammers
David K
DK
Hawkins
Alastair R
AR
D001233:Aspergillus nidulans / Q000201:enzymology / Q000378:metabolism*; D001483:Base Sequence; D002152:Calorimetry, Differential Scanning; D017931:DNA Primers; D005656:Fungal Proteins; D008958:Models, Molecular; D010084:Oxidation-Reduction; D012097:Repressor Proteins / Q000502:physiology*
D017931:DNA Primers; D005656:Fungal Proteins; C441635:NmrA protein, Aspergillus nidulans; D012097:Repressor Proteins