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Structure of the orthorhombic crystal form of human alanine:glyoxylate aminotransferase

Human alanine:glyoxylate aminotransferase (AGT) is a homodimeric pyridoxal 5'-phosphate (PLP-) dependent enzyme which catalyzes the transamination reaction between L-alanine and glyoxylate to produce pyruvate and glycine. Either deficiency or malfunctioning of this liver-specific peroxisomal enzyme causes primary hyperoxaluria type 1 (PH1), an autosomal recessive disorder in which accumulated glyoxylate oxidizes to oxalate. Finally, oxalate deposes as insoluble calcium oxalate in the kidney and urinary tract. The structure of human AGT in complex with the competitive inhibitor amino-oxyacetic acid was previously determined to 2.5 Å resolution (tetragonal crystal form, space group P41212, unit-cell parameters: a = 90.3 Å and c = 142.0 Å ) with one 392-residue polypeptide chain (a half of the biologically active dimer) in the crystallographic asymmetric unit [X. Zhang et al., J. Mol. Biol. 331 (2003) 643]. We present the X-ray crystal structures of human AGT in complex with L-alanine and D-alanine, respectively, determined to 2.0 Å resolution. The modified conditions used for AGT crystallization resulted in the orthorhombic crystal form (space group P212121, unit-cell parameters: a = 126.4 Å , b = 140.8 Å and c = 253.7 Å ) with four protein dimers in the asymmetric unit. Comparison of the eight crystallographically independent active sites in the orthorhombic crystal form of AGT gives us information about the conformational flexibility of the active-site residues thus providing an additional insight in the structural basis for the catalytic mechanism of AGT.

Structure of the orthorhombic crystal form of human alanine:glyoxylate aminotransferase

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