The Structural Biology Research Of ARO9 From Saccharomyces Cerevisiae & Human ZO-2 PDZ2

The PLP-dependent enzymes are the enzymes which use pyridoxal-5'-phosphate as cofactor.They are widely distributed in nature,and catalyze a large variety of reactions.These enzymes are principally participated in the catabolism and the anabolism of amino acids and amino acid-derived metabolites.Based on the solved structure,all the PLP enzymes are divided into five fold types:the fold typeⅠ(aspartate aminotransferase family),the fold typeⅡ(tryptophan synthase family),the fold typesⅢ(alanine racemase family),the fold typeⅣ(D-amino acid aminotransferase family) and the fold typeⅤ(glycogen phosphorylase family).The aminotransferases catalyze the reversible transfer of amino groups from amino acids to oxo acids.This is vital for the metabolism of amino acids.Based on the substrate specificity and the sequence specificity,these aminotransferases are divided into four subfamilies.Saccharomyces cerevisae ARO9 protein,an aromatic aminotransferaseⅡ,belongs to the aminotransferase subfamilyⅠ.It catalyzes the transamination step of the catabolism of aromatic amino acids.We reported the crystal structure of ARO9,determined by molecular replacement method at 2.4(?).The crystal structure of ARO9 consists by three regions:the N-terminal region, the large domain and the small domain.The large and small domains are conserved among the aspirated aminotransferase.The large domain contains a seven-strandedβ-sheet and 16 helices.And the small domain comprises the C-terminal part,which folds into three-strandedβ-sheet and 5 helices.Three dimensional structure comparisons revealed that the major difference in protein folding to be at the N-terminal residues.In ARO9,there are two antiparallelβstrands.The region is critical in forming the homodimer of ARO9.Alignments of the sequence and structure of ARO9 with other aminotransferase indicated that ARO9 and hKatⅡactually form a new subgroup in subfamilyⅠaminotransferase.It also indicated that the residues in the catalytic sites were lacated at the same spatial positions as hKatⅡ. (2) Human ZO-2 protein is a multi-domain protein consisting of an SH3 domain, a GUK domain and three copies of PDZ domain with slightly divergence.The three PDZ domains act as protein-recognition modules that may mediate protein assembly and subunit localization.The crystal structure of the second PDZ domain of ZO-2 (ZO-2 PDZ2) was determined by molecular replacement,revealing a dimer per asymmetric unit at 1.75(?) resolution.The dimer is stabilized by extensive symmetrical domain-swapping ofβ1 andβ2 strands.Structural comparison and docking show that ZO-2 PDZ2 homodimer might have a difference ligand-binding pattern to the classic PDZ binding pattern.