Journal
PROTEIN SCIENCE
Volume 14, Issue 6, Pages 1498-1507Publisher
WILEY
DOI: 10.1110/ps.051397905
Keywords
pyridoxal-5 '-phosphate; Schiff base; phosphoserine aminotransferase.; radiation damage
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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 angstrom 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) G gamma. 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.
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