Three-dimensional structure of tyrosine phenol-lyase
Tyrosine phenol-lyase (EC 22.214.171.124) from Citrobacter freundii has been cloned and the primary sequence deduced from the DNA sequence. From the BrCN digest of the NaBH4-reduced holoenzyme, five peptides were purified and sequenced. The amino acid sequences of the peptides agreed with the corresponding parts of the tyrosine phenol-lyase sequence obtained from the gene structure. K257 is the pyridoxal 5'-phosphate binding residue. Assisted by the sequence data, the crystal structure of apotyrosine
... ture of apotyrosine phenol-lyase, a pyridoxal 5'-phosphate-dependent enzyme, has been refined to an R-factor of 16.2% at 2.3-%L resolution using synchrotron radiation diffraction data. The tetrameric molecule has 222 symmetry, with one of the axes coincident with the cr stallographic 2-fold symmetry axis of the crystal which belongs to the space group P2,212 with a = 76.0 l, b = 138.3 A, and c = 93.5 A. Each subunit comprises 14 a-helices and 16 &strands, which fold into a small and a large domain. The coenzyme-binding lysine residue is located at the interface between the large and small domains of one subunit and the large domain of a crystallographically related subunit. The fold of the large, pyridoxal 5'-phosphate binding domain and the location of the active site are similar to that found in aminotransferases. Most of the residues which participate in binding of pyridoxal 5'-phosphate in aminotransferases are conserved in the structure of tyrosine phenol-lyase. Two dimers of tyrosine phenol-lyase, each of which has a domain architecture similar to that found in aspartate aminotransferases, are bound together through a hydrophobic cluster in the center of the molecule and intertwined N-terminal arms. Pyridoxal 5'-phosphate-(PLP-) * containing enzymes perform a variety of reactions in the metabolic pathways of amino acids, including transamination, 8and y-elimination and replacement, decarboxylation, and racemization. Tyrosine phenol-lyase (TPL; EC 126.96.36.199) is a PLP-dependent enzyme that catalyzes the 0-elimination of L-tyrosine to give phenol and ammonium pyruvate (Kumagai et al., 1970a,b). The molecule of TPL consists of four chemically identical subunits (Kazakov et al., 1987), each with molecular mass about 50 kDa, and binds 4 mol of PLP per tetramer. This enzyme is found primarily in enterobacteria (Enei et al., 1972), although it has been reported to occur in some arthropods (Duffey & Blum, 1977; Duffey et al., 1977). A.A.A. thanks the EMBL, Hamburg, for a fellowship supporting this work. I Abbreviations: PLP, pyridoxal 5'-phosphate; TPL, tyrosine phenollyase (EC 4 .1.99.2) ; AspAT, aspartate aminotransferase; TRPase, tryptophan indole-lyase (tryptophanase) (EC 188.8.131.52) . Heslington, York YO1 SDD, England. University of Georgia. X-ray analyses of PLP-dependent enzymes from several different classes are presently underway. X-ray crystallographic studies have been carried out on a number of aminotransferases [full references are given in Fukui et al.