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1.  Threonine 57 is required for the post-translational activation of Escherichia coli aspartate α-decarboxylase 
Threonine 57 is identified as the key residue required for the post-translational activation of E. coli aspartate decarboxylase. The crystal structure of the site-directed mutant T57V is reported.
Aspartate α-decarboxylase is a pyruvoyl-dependent decarboxylase required for the production of β-alanine in the bacterial pantothenate (vitamin B5) biosynthesis pathway. The pyruvoyl group is formed via the intramolecular rearrangement of a serine residue to generate a backbone ester intermediate which is cleaved to generate an N-terminal pyruvoyl group. Site-directed mutagenesis of residues adjacent to the active site, including Tyr22, Thr57 and Tyr58, reveals that only mutation of Thr57 leads to changes in the degree of post-translational activation. The crystal structure of the site-directed mutant T57V is consistent with a non-rearranged backbone, supporting the hypothesis that Thr57 is required for the formation of the ester intermediate in activation.
PMCID: PMC3975893  PMID: 24699660
aspartate decarboxylase; post-translational modification; amino-acid-derived cofactors; pyruvoyl-dependent
2.  X-ray-excited optical luminescence of protein crystals: a new tool for studying radiation damage during diffraction data collection 
During X-ray irradiation protein crystals radiate energy in the form of small amounts of visible light. This is known as X-ray-excited optical luminescence (XEOL). The XEOL of several proteins and their constituent amino acids has been characterized using the microspectrophotometers at the Swiss Light Source and Diamond Light Source. XEOL arises primarily from aromatic amino acids, but the effects of local environment and quenching within a crystal mean that the XEOL spectrum of a crystal is not the simple sum of the spectra of its constituent parts. Upon repeated exposure to X-rays XEOL spectra decay non-uniformly, suggesting that XEOL is sensitive to site-specific radiation damage. However, rates of XEOL decay were found not to correlate to decays in diffracting power, making XEOL of limited use as a metric for radiation damage to protein crystals.
PMCID: PMC3370260  PMID: 22525748
3.  Revealing low-dose radiation damage using single-crystal spectroscopy 
Journal of Synchrotron Radiation  2011;18(Pt 3):367-373.
Data on the rapid reduction of haem proteins in the X-ray beam at synchrotron sources are presented. The use of single-crystal spectroscopy to detect these changes and their implication for diffraction data collection from oxidized species is also discussed.
The structural information and functional insight obtained from X-ray crystallography can be enhanced by the use of complementary spectroscopies. Here the information that can be obtained from spectroscopic methods commonly used in conjunction with X-ray crystallography and best-practice single-crystal UV-Vis absorption data collection are briefly reviewed. Using data collected with the in situ system at the Swiss Light Source, the time and dose scales of low-dose X-ray-induced radiation damage and solvated electron generation in metalloproteins at 100 K are investigated. The effect of dose rate on these scales is also discussed.
PMCID: PMC3083913  PMID: 21525644
macromolecular crystallography; single-crystal microspectrophotometry; radiation damage; myoglobin; cytochrome c

Results 1-3 (3)