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Construction, Purification and Characterization of Untagged Human Liver Alanine-Glyoxylate Aminotransferase Expressed in Escherichia coli

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His-tagging is commonly used to aid and expedite the purification of recombinant proteins. It is commonly assumed, though less frequently tested, that the His-tag affects neither the structure nor the stability of the protein. Alanine:glyoxylate aminotransferase (AGT) is a peroxisomal pyridoxal 5'-phosphate (PLP) dependent enzyme which catalyzes the transamination of alanine and glyoxylate to pyruvate and glycine. AGT is a clinically relevant enzyme whose deficiency causes an inherited rare metabolic disorder named primary hyperoxaluria type I. Until now, the structure and function of this enzyme have been studied using recombinant wild-type AGT and variants purified using a hexahistidine tag. However, the study of the functional roles of the N- and C-termini in the dimerization process and on the import into the peroxisome, respectively, requires the preparation of human liver AGT without histidine tags. We report for the first time the expression of untagged AGT together with a new rapid protocol for its purification. In addition, the kinetic parameters for the forward and reverse transamination catalyzed by untagged AGT as well as the spectroscopic features, the KD(PLP), the pH and thermal stability of the enzyme in the holo- and apo-form have been determined. This investigation will be the starting point for a detailed understanding of the contributions of the N- and C-termini on the dimerization and folding of AGT, and on its import into the peroxisome. This is prerequisite to understand how pathological mutations affect the proper native quaternary and tertiary structure, stability, and targeting of the enzyme.

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Keywords: Alanine; glyoxylate aminotransferase; histidine-tag; pyridoxal 5'-phosphate; thermal stability

Document Type: Research Article

Publication date: 2008-02-01

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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