Strain relief at the active site of phosphoserine aminotransferase induced by radiation damage.
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Dubnovitsky AP, Ravelli RB, Popov AN, Papageorgiou AC
Strain relief at the active site of phosphoserine aminotransferase induced by radiation damage.
Protein Sci. 2005 Jun;14(6):1498-507. Epub 2005 May 9.
- PubMed ID
- 15883191 [ View in PubMed]
- Abstract
The X-ray susceptibility of the lysine-pyridoxal-5'-phosphate Schiff base in Bacillus alcalophilus phosphoserine aminotransferase has been investigated using crystallographic data collected at 100 K to 1.3 A resolution, complemented by on-line spectroscopic studies. X-rays induce deprotonation of the internal aldimine, changes in the Schiff base conformation, displacement of the cofactor molecule, and disruption of the Schiff base linkage between pyridoxal-5'-phosphate and the Lys residue. Analysis of the "undamaged" structure reveals a significant chemical strain on the internal aldimine bond that leads to a pronounced geometrical distortion of the cofactor. However, upon crystal exposure to the X-rays, the strain and distortion are relaxed and eventually diminished when the total absorbed dose has exceeded 4.7 x 10(6) Ggamma. Our data provide new insights into the enzymatic activation of pyridoxal-5'-phosphate and suggest that special care should be taken while using macromolecular crystallography to study details in strained active sites.