engleski

Discrete disorder of a whole protein domain in the crystals of tyrosine phenol-lyase

Tyrosine phenol-lyase (TPL) is a homotetrameric pyridoxal-5’ -phosphate (PLP)-dependent enzyme that catalyses the reversible hydrolytic cleavage of L-tyrosine to phenol and ammonium pyruvate (the β -elimination of L-tyrosine) [R. S. Phillips, T. V. Demidkina, N. G. Faleev, Biochim. Biophys. Acta, 1647 (2003) 167]. As shown previously [D. Milić, D. Matković-Čalogović, T. V. Demidkina, V. V. Kulikova, N. I. Sinitzina, A. A. Antson, Biochemistry, 45 (2006) 7544], TPL crystallises in the space group P2(1)2(1)2 with two protein subunits (the catalytic dimer) in the asymmetric unit. In the structure of TPL holoform all protein subunits are in the open conformation. Contrary, in the structure of TPL apoform one protein subunit of the catalytic dimer is in the open conformation, while the other is found in the closed conformation with a significant part of the small protein domain moved toward the large domain. By this domain movement certain catalytically important residues are brought into the active site and the active site cleft becomes closed. We also determined crystal structures of several TPL complexes with bound small molecules which resemble certain enzymatic reaction intermediates. For some of these structures the discrete disorder of the small protein domain was clearly observed in the electron density maps. Namely, the small TPL domain of one protein subunit in the catalytic dimer is present in both closed and open conformation (approximately 50% of each). To our best knowledge, this is the first example of discrete static disorder of a whole protein domain in a protein crystal structure. Modelling and refinement of such disorder will be discussed.

disorder; protein crystallography; tyrosine phenol-lyase

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