4O1Q: Crystal Structure Of The Q103n-maug/pre-methylamine Dehydrogenase Complex

Citation:
Abstract
The diheme enzyme MauG catalyzes a six-electron oxidation that is required for the posttranslational modification of a precursor of methylamine dehydrogenase (preMADH) to complete the biosynthesis of its protein-derived cofactor, tryptophan tryptophylquinone (TTQ). Crystallographic and computational studies have implicated Gln103 in stabilizing the Fe(IV) horizontal lineO moiety of the bis-Fe(IV) state by hydrogen bonding. The role of Gln103 was probed by site-directed mutagenesis. Q103L and Q103E mutations resulted in no expression and very little expression of the protein, respectively. Q103A MauG exhibited oxidative damage when isolated. Q103N MauG was isolated at levels comparable to that of wild-type MauG and exhibited normal activity in catalyzing the biosynthesis of TTQ from preMADH. The crystal structure of the Q103N MauG-preMADH complex suggests that a water may mediate hydrogen bonding between the shorter Asn103 side chain and the Fe(IV) horizontal lineO moiety. The Q103N mutation caused the two redox potentials associated with the diferric/diferrous redox couple to become less negative, although the redox cooperativity of the hemes of MauG was retained. Upon addition of H2O2, Q103N MauG exhibits changes in the absorbance spectrum in the Soret and near-IR regions consistent with formation of the bis-Fe(IV) redox state. However, the rate of spontaneous return of the spectrum in the Soret region was 4.5-fold greater for Q103N MauG than for wild-type MauG. In contrast, the rate of spontaneous decay of the absorbance at 950 nm, which is associated with charge-resonance stabilization of the high-valence state, was similar for wild-type MauG and Q103N MauG. This suggests that as a consequence of the mutation a different distribution of resonance structures stabilizes the bis-Fe(IV) state. These results demonstrate that subtle changes in the structure of the side chain of residue 103 can significantly affect the overall protein stability of MauG and alter the redox properties of the hemes.
PDB ID: 4O1QDownload
MMDB ID: 119766
PDB Deposition Date: 2013/12/16
Updated in MMDB: 2014/05
Experimental Method:
x-ray diffraction
Resolution: 2.59  Å
Source Organism:
Similar Structures:
Biological Unit for 4O1Q: hexameric; determined by author and by software (PISA)
Molecular Components in 4O1Q
Label Count Molecule
Proteins (6 molecules)
2
Methylamine Utilization Protein Maug
Molecule annotation
2
Methylamine Dehydrogenase Light Chain
Molecule annotation
2
Methylamine Dehydrogenase Heavy Chain
Molecule annotation
Chemicals (14 molecules)
1
2
2
4
3
3
4
1
5
1
6
2
7
1
* Click molecule labels to explore molecular sequence information.

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