Structural highlights
Function
[ULAG_ECOLI] Probably catalyzes the hydrolysis of L-ascorbate-6-P into 3-keto-L-gulonate-6-P. Is essential for L-ascorbate utilization under anaerobic conditions. Also shows phosphodiesterase activity, hydrolyzing phosphodiester bond in the artificial chromogenic substrate bis-p-nitrophenyl phosphate (bis-pNPP).[1] [2]
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
The ulaG gene, located in the ula regulon, is crucial for the catabolism of l-ascorbate under anaerobic conditions and it has been proposed to encode for the putative l-ascorbate-6-P lactonase. The ulaG gene is widespread among eubacteria, including human commensal and pathogenic genera such as Escherichia, Shigella, Klebsiella and Salmonella. Here, we report the three-dimensional structures of the apoenzyme and Mn(2+) holoenzyme of UlaG from E. coli to 2.6 A resolution, determined using single-wavelength anomalous diffraction phasing and molecular replacement, respectively. The structures reveal a highly specialized metallo-beta-lactamase-like fold derived from an ancient structural template that was involved in RNA maturation and DNA repair. This fold has a novel quaternary architecture consisting of a hexameric ring formed by a trimer of UlaG dimers. A mononuclear Mn(2)(+)-binding site resides at the core of the active site, which displays micromolar affinity for Mn(2+) and a distorted trigonal bipyramidal coordination. The active site Mn(2+) ion can be replaced by Co(2+) or Zn(2+), but not by Fe(3+). We further show that the Mn(2+) or Co(2)(+)-loaded enzyme exhibits lactonase activity towards l-ascorbate 6-P, thereby providing the first direct evidence of its catalytic role in the L-ascorbate catabolic pathway. Guided by the structural homology, we show that UlaG is able to cleave phosphodiester linkages in cyclic nucleotides, suggesting that the conservation of the fold and of the key catalytic residues allows for the evolutionary acquisition of substrate specificity for novel but related substrates.
Molecular architecture of the Mn2+-dependent lactonase UlaG reveals an RNase-like metallo-beta-lactamase fold and a novel quaternary structure.,Garces F, Fernandez FJ, Montella C, Penya-Soler E, Prohens R, Aguilar J, Baldoma L, Coll M, Badia J, Vega MC J Mol Biol. 2010 May 21;398(5):715-29. Epub 2010 Mar 30. PMID:20359483[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Zhang Z, Aboulwafa M, Smith MH, Saier MH Jr. The ascorbate transporter of Escherichia coli. J Bacteriol. 2003 Apr;185(7):2243-50. PMID:12644495
- ↑ Kuznetsova E, Proudfoot M, Sanders SA, Reinking J, Savchenko A, Arrowsmith CH, Edwards AM, Yakunin AF. Enzyme genomics: Application of general enzymatic screens to discover new enzymes. FEMS Microbiol Rev. 2005 Apr;29(2):263-79. PMID:15808744 doi:S0168-6445(05)00004-5
- ↑ Garces F, Fernandez FJ, Montella C, Penya-Soler E, Prohens R, Aguilar J, Baldoma L, Coll M, Badia J, Vega MC. Molecular architecture of the Mn2+-dependent lactonase UlaG reveals an RNase-like metallo-beta-lactamase fold and a novel quaternary structure. J Mol Biol. 2010 May 21;398(5):715-29. Epub 2010 Mar 30. PMID:20359483 doi:10.1016/j.jmb.2010.03.041
