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| IJCEM Copyright © 2008-All rights reserved. Published by e-Century Publishing Corporation, Madison, WI 53711 |
Int J Clin Exp Med 1(3),248-259;2009
Original Article
The Differential Effects of R580A Mutation on Transamidation and GTP Binding
Activity of Rat and Human Type 2 Transglutaminase
Qingmin Ruan, Janusz Tucholski, Soner Gundemir and Gail V.W. Johnson Voll
Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294-0017, USA;
Department of Anesthesiology and Department of Pharmacology and Physiology University of Rochester, Rochester, NY 14642, USA
Received May 3, 2008; accepted June 21, 2008; available online June 30, 2008
Abstract: Type 2 transglutaminase (TG2) is an acyltransferase, which also undergoes a GTP-binding/GTPase cycle, with guanine
nucleotide and calcium binding reciprocally regulating its transamidation (TG) activity. TG2 is expressed ubiquitously throughout the
human body and is the predominant neuronal transglutaminase. Given a postulated role for TG2 in a number of physiological and
pathological processes including neurodegenerative diseases, it is of critical importance to understand how TG2 and its enzymatic
activities are regulated in the cells. The various aspects of TG2 regulation are addressed by using rat and human TG2 proteins,
however, despite their homologous structure, regulation of their enzymatic activities may differ, especially in the cellular context. Here,
we evaluate the role of Arg580 in human TG2 and Arg579 in rat TG2 in modulating GTP binding and TG activities in vitro and in situ. We
confirm the importance of Arg580 and Arg579 in TG2 for GTP binding as their mutation to Ala completely abolished GTP binding activity
in both human (R580A) and rat TG2 (R579A). Next, we showed that in transfected human embryonic kidney (HEK) 293 cells, basal in
situ TG activity of human R580A TG2 and rat R579A TG2 was significantly greater than their wild-type (WT) counterparts. However, TG
activity of the mutants and WT TG2 became equivalent when the intracellular calcium concentration was maximally increased with
maitotoxin. Also, in vitro TG activity assay revealed an intriguing difference between rat and human TG2; at a calcium concentration
when their activities were maximum, the protein level of human R580A TG2 was lower than its WT counterpart, whereas rat R579A and
WT TG2 protein levels were similar. Taken together, our study underscores an essential role of Arg580 in human TG2 and Arg579 in rat
TG2 for their GTP binding ability and also describes for the first time that these amino acid residues differentially influence the TG
activity of human or rat TG2 by calcium in vitro and in situ. (IJCEM805002).
Key Words: type 2 transglutaminase, tTG, tissue transglutaminase, Arg580, Arg579, GTP binding, transamidation activity, R580A,
R579A
Full Text PDF
Address all correspondence to: Janusz Tucholski, PhD, Department of Psychiatry and Behavioral Neurobiology, 1720 7th Avenue
South, SC981, University of Alabama at Birmingham, Birmingham, AL 35294-0017, USA; Tel: 205 934-2144; Fax: 205 934-2500;
E-mail: jtuchol@uab.edu
Original Article
The Differential Effects of R580A Mutation on Transamidation and GTP Binding
Activity of Rat and Human Type 2 Transglutaminase
Qingmin Ruan, Janusz Tucholski, Soner Gundemir and Gail V.W. Johnson Voll
Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294-0017, USA;
Department of Anesthesiology and Department of Pharmacology and Physiology University of Rochester, Rochester, NY 14642, USA
Received May 3, 2008; accepted June 21, 2008; available online June 30, 2008
Abstract: Type 2 transglutaminase (TG2) is an acyltransferase, which also undergoes a GTP-binding/GTPase cycle, with guanine
nucleotide and calcium binding reciprocally regulating its transamidation (TG) activity. TG2 is expressed ubiquitously throughout the
human body and is the predominant neuronal transglutaminase. Given a postulated role for TG2 in a number of physiological and
pathological processes including neurodegenerative diseases, it is of critical importance to understand how TG2 and its enzymatic
activities are regulated in the cells. The various aspects of TG2 regulation are addressed by using rat and human TG2 proteins,
however, despite their homologous structure, regulation of their enzymatic activities may differ, especially in the cellular context. Here,
we evaluate the role of Arg580 in human TG2 and Arg579 in rat TG2 in modulating GTP binding and TG activities in vitro and in situ. We
confirm the importance of Arg580 and Arg579 in TG2 for GTP binding as their mutation to Ala completely abolished GTP binding activity
in both human (R580A) and rat TG2 (R579A). Next, we showed that in transfected human embryonic kidney (HEK) 293 cells, basal in
situ TG activity of human R580A TG2 and rat R579A TG2 was significantly greater than their wild-type (WT) counterparts. However, TG
activity of the mutants and WT TG2 became equivalent when the intracellular calcium concentration was maximally increased with
maitotoxin. Also, in vitro TG activity assay revealed an intriguing difference between rat and human TG2; at a calcium concentration
when their activities were maximum, the protein level of human R580A TG2 was lower than its WT counterpart, whereas rat R579A and
WT TG2 protein levels were similar. Taken together, our study underscores an essential role of Arg580 in human TG2 and Arg579 in rat
TG2 for their GTP binding ability and also describes for the first time that these amino acid residues differentially influence the TG
activity of human or rat TG2 by calcium in vitro and in situ. (IJCEM805002).
Key Words: type 2 transglutaminase, tTG, tissue transglutaminase, Arg580, Arg579, GTP binding, transamidation activity, R580A,
R579A
Full Text PDF
Address all correspondence to: Janusz Tucholski, PhD, Department of Psychiatry and Behavioral Neurobiology, 1720 7th Avenue
South, SC981, University of Alabama at Birmingham, Birmingham, AL 35294-0017, USA; Tel: 205 934-2144; Fax: 205 934-2500;
E-mail: jtuchol@uab.edu
