Activation of transglutaminase in mu-calpain null erythrocytes.
Intracellular transglutaminases (protein-glutamine: amine gamma-glutamyltransferase, EC 2.3.2.13) are calcium-dependent thiol enzymes that catalyze the covalent cross-linking of proteins, including those in the erythrocyte membrane. Several studies suggest that the activation of some transglutaminases is positively regulated by the calcium-dependent cysteine protease, mu-calpain. Using mu-calpain null (Capn1(-/-)) mouse erythrocytes, we demonstrate that the activation of soluble as well as membrane-bound forms of transglutaminase (TG2) in mouse erythrocytes was independent of mu-calpain. Also, the absence of mu-calpain or any detectable cysteine protease did not affect the transglutaminase activity in the erythrocyte lysate. Our studies also identify physiological substrates of mu-calpain in the erythrocyte membrane and show that their cleavage has no discernible effect on the transglutaminase mediated cross-linking of membrane proteins. Taken together, these data suggest the existence of a calpain-independent mechanism for the activation of transglutaminase 2 by calcium ions in the mouse erythrocytes and presumably also in non-erythroid cells.
O'Neill
Gerald M
GM
Department of Medicine, Center for Biomedical Research, CBR 404, St. Elizabeth's Medical Center, Tufts University School of Medicine, Boston, MA 01235-29, USA.
Prasanna Murthy
S N
SN
Lorand
Laszlo
L
Khanna
Richie
R
Liu
Shih-Chun
SC
Hanspal
Manjit
M
Hanada
Toshihiko
T
Chishti
Athar H
AH
D000818:Animals; D002118:Calcium; D002154:Calpain / Q000235:genetics / Q000502:physiology*; D004789:Enzyme Activation; D004912:Erythrocytes / Q000201:enzymology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases / Q000378:metabolism*
D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D002154:Calpain; C449002:mu-calpain; D019204:GTP-Binding Proteins; D002118:Calcium