title: Strain relief at the active site of phosphoserine aminotransferase induced by radiation damage.
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.
authors.affiliation: Turku Centre for Biotechnology, University of Turku, Finland.
authors.forename: Anatoly P
authors.initials: AP
authors.lastname: Dubnovitsky
authors.forename: Raimond B G
authors.initials: RB
authors.lastname: Ravelli
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Popov
authors.forename: Anastassios C
authors.initials: AC
authors.lastname: Papageorgiou
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D018360:Crystallography, X-Ray; D008239:Lysine / Q000737:chemistry; D011732:Pyridoxal Phosphate / Q000737:chemistry; D012545:Schiff Bases / Q000737:chemistry; D000637:Transaminases / Q000737:chemistry*
chemical_list: D012545:Schiff Bases; D011732:Pyridoxal Phosphate; D000637:Transaminases; C022393:phosphoserine aminotransferase; D008239:Lysine