1. Alcaligenes faecalis Arsenite Oxidase A new molybdenum protein structure from beamline 9-2
By Paul Ellis

2. What we knew
Induced in A. faecalis by the presence of arsenite (AsO2-).
Oxidizes arsenite to the less-toxic arsenate (AsO43-): AsIIIO2- + 2H2O  AsVO H+ + 2e-
DMSO reductase family:
HiPIP: mV reduction potential
Rieske: mV reduction potential
AsVO43-/AsIIIO2-: +60 mV
CO2/HCOOH: -200 mV
DMSO/DMS: +160 mV
TMAO/TMA: 
NO3-/NO2-: 
DMSO reductase from R. sphaeroides
Mo(VI/V): +144 mV
Mo(V/IV): +160 mV Mo Mo Mo
4Fe/4S
4Fe/4S HiPIP
or 3Fe/4S
Rieske 2Fe/2S
DMSO Reductase, TMAO Reductase
Formate Dehydrogenase
Arsenite Oxidase

3. Arsenite oxidase crystals
Cell solvent content
P1 triclinic 59%
P21 monoclinic 57%
P2 monoclinic 56%
C2 monoclinic 71%
I222 orthorhombic -5%
P4 tetragonal 33%
P4x212 tetragonal 18%
R32 trigonal 58%

4. Mercury derivatives of the P1 form

5. Phased anomalous map from SHARPHg Mo Fe Fe

6. Beamline 9-2

7. MAD data collection from a P21 crystal
low energy = 6900 eV
maximum f’’
minimum f’
high energy = eV

8. Locating the metal atoms in the P21 cell
superpose

9. Picking the correct solution
Incorrect
Correct

10. Backbone autotraced by wARP

11. Sequencing
Sequence based on electron density and hydrogen-bonding patterns
ASP=ASN GLU=GLN
95% of residues assigned
Matches known N-terminal sequence of the long chain

12. Final model

13. Acknowledgements
Department of Molecular Biochemistry, Ohio State University
Russ Hille
Thomas Conrads
Structural Molecular Biology, SSRL
Peter Kuhn
Mike Soltis
Aina Cohen
Tim McPhillips
Henry Bellamy
Department of Energy:
Office of Basic Energy Sciences
Office of Biological and Environmental Research
National Institutes of Health, National Center for Research Resources, Biomedical Technology Program

14. Summary Phased using data from two crystal forms.
Sequenced approximately 95% of residues based on density and hydrogen bonding.
Protein consists of a long chain containing the Mo site and a 3Fe/4S cluster and a short chain containing a Rieske-type 2Fe/2S site.
Long chain is homologous to other members of the DMSO reductase family, but there is no protein sidechain bound to Mo.
Short chain has no counterpart among known Mo protein structures but is similar to the Rieske Fe/S protein domains of:
cytochrome bc1
cytochrome b6f
naphthalene 1,2‑dioxygenase.