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Renal gamma-glutamyl transpeptidases: structural and immunological studies
S S Tate1, V Khadse, D Wellner
1Department of Biochemistry, Cornell University Medical College, New York, New York 10021.
Archives of Biochemistry and Biophysics
|May 1, 1988
Summary
Mammalian kidney gamma-glutamyl transpeptidases show significant amino-terminal sequence homology, especially in the small subunit, indicating conserved function. Species variations are mainly due to protein glycosylation, not core structural differences.
Area of Science:
- Biochemistry
- Enzymology
- Comparative analysis of mammalian kidney enzymes
Background:
- Mammalian kidney gamma-glutamyl transpeptidases (GGTs) are crucial enzymes involved in amino acid transport and glutathione metabolism.
- Variations in GGTs across species can impact their catalytic properties and physiological roles.
- Understanding the structural basis of these variations is key to comprehending enzyme function and evolution.
Purpose of the Study:
- To compare mammalian kidney gamma-glutamyl transpeptidases from different species.
- To investigate the structural basis for species-related variations in GGTs, focusing on subunit characteristics and immunological properties.
- To elucidate the evolutionary conservation and functional implications of GGT structure.
Main Methods:
- Comparative analysis of subunit size, amino-terminal sequences, and immunological properties of kidney gamma-glutamyl transpeptidases.
- Use of antibodies raised against native and deglycosylated enzyme subunits.
- Amino acid sequencing of heavy and small subunits from rat, bovine, dog, and human kidney transpeptidases.
- Assessment of catalytic properties, including acceptor specificity and inactivation by AT-125 (acivicin).
Main Results:
- Species-related variations in apparent molecular weight are primarily attributed to differences in protein glycosylation.
- Immunological studies reveal shared antigenic determinants among transpeptidases, with some requiring deglycosylation for detection.
- High homology was observed in the amino-terminal sequences of both heavy and small subunits across species, particularly the first 23 residues of the small subunit (91-96% identity).
- The identical first 7 residues of the small subunit suggest specific proteolytic processing of the precursor.
Conclusions:
- Mammalian kidney gamma-glutamyl transpeptidases share significant structural and immunological similarities, indicating a conserved functional core.
- Protein glycosylation is a major factor contributing to observed species-specific differences in molecular weight.
- Subtle structural variations in the active center, likely in the small subunit, account for differences in substrate specificity and inhibitor susceptibility.