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Hypotheses
1) arsC evolved after araA/araB since a reducing environment existed pre-dating the necessity for the reductase activity encoded by arsC.
2) ArsA, arsB and arsC should be highly conserved given their ubiquity in all three domains.
3) Non-ATP dependent AraB should be structurally different from ATP-dependent AraB.
4) The phlyogenetic relationships between ara genes should reflect the 16S rRNA phylogenies.
Results
1) arsC sequences are very dissimiliar between Archaea and bacteria. Indeed, sequences search do not recover any ArsC Archaea genes, although several species are known to contain them.
2) ArsA and arsB phylogenetically grouped with species in the Eubacteria, Archaea and Eukarya domains suggesting that other than structural constraints around the active site, there is much less conservation elsewhere.
3) The branches in the phylogenetic trees are very short indicating little conservation of sequence.
Student research
Bioinformatics
1)Do a thorough search for ArsC sequeneces. Most likely there will be new sequences online as interest in Archaean speicies is high.
2) Syntenic chromosome structure for the ars operon should be quite interesting since lateral gene exchange and homologous recombination have driven evolution of arsenate resistance across domains.
3) ArsA has an internal duplication of ATPase domains in most species investigated. It would be most interesting to explore this feature of gene structure.
Biochemistry
1) Mutations have been documented in E coli. Biochemical analysis of the relationship of arsenate resistance to gene structure will clarify structural constraints.
2) Selection of arsenate resistance mutants, using recombinant plasmids with heterologous sequences are all techniques that are accessible to student research.
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References
Crameri A, Dawes G, Rodriguez E Jr, Silver S, Stemmer WP. 1997. Molecular evolution of an arsenate detoxification pathway by DNA shuffling. Nat Biotechnol.:15(5):436-8.
Colin R. Jackson and Sandra L. Dugas. 2003. Phylogenetic analysis of bacterial and archaeal arsC gene sequences
suggests an ancient, common origin for arsenate reductase. BMC Evolutionary Biology. 3:18-28.
Diorio, C., J. Cai, et al. 1995. "An Escherichia coli chromosomal ars operon homolog is functional in arsenic detoxification and is conserved in gram-negative bacteria." J. Bacteriol. 177: 2050-2056.
Marchler-Bauer A, Panchenko AR, Shoemaker BA, Thiessen PA, Geer LY, Bryant SH. 2002. CDD: a database of conserved domain alignments with links to domain three-dimensional structure. Nucleic Acids Res. 30(1):281-3.
Marchler-Bauer A, Anderson JB, Derbyshire MK, DeWeese-Scott C, Gonzales NR, Gwadz M, Hao L, He S, Hurwitz DI, Jackson JD, Ke Z, Krylov D, Lanczycki CJ, Liebert CA, Liu C, Lu F, Lu S, Marchler GH, Mullokandov M, Song JS, Thanki N, Yamashita RA, Yin JJ, Zhang D, Bryant SH. 1997. CDD: a conserved domain database for interactive domain family analysis. Nucleic Acids Res. 35(Database issue):D237-40. Epub 2006 Nov 29.
Saltikov, C. W. and B. H. Olson (2002). "Homology of Escherichia coli R773 arsA, arsB, and arsC Genes in Arsenic-Resistant Bacteria Isolated from Raw Sewage and Arsenic-Enriched Creek Waters." Appl. Environ. Microbiol. 68(1): 280-288.
Sato, T. and Y. Kobayashi. 1998. "The ars Operon in the skin Element of Bacillus subtilis Confers Resistance to Arsenate and Arsenite." J. Bacteriol. 180(7): 1655-1661.
Zhou, T., B. P. Rosen, et al. 1999. "Crystallization and preliminary X-ray analysis of the catalytic subunit of the ATP-dependent arsenite pump encoded by the Escherichia coli plasmid R773." Acta Cryst. D55: 921-924.
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