title: Activation of transglutaminase in mu-calpain null erythrocytes.
abstract: 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.
authors.affiliation: Department of Medicine, Center for Biomedical Research, CBR 404, St. Elizabeth's Medical Center, Tufts University School of Medicine, Boston, MA 01235-29, USA.
authors.forename: Gerald M
authors.initials: GM
authors.lastname: O'Neill
authors.forename: S N
authors.initials: SN
authors.lastname: Prasanna Murthy
authors.forename: Laszlo
authors.initials: L
authors.lastname: Lorand
authors.forename: Richie
authors.initials: R
authors.lastname: Khanna
authors.forename: Shih-Chun
authors.initials: SC
authors.lastname: Liu
authors.forename: Manjit
authors.initials: M
authors.lastname: Hanspal
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Hanada
authors.forename: Athar H
authors.initials: AH
authors.lastname: Chishti
mesh_terms: 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*
chemical_list: D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D002154:Calpain; C449002:mu-calpain; D019204:GTP-Binding Proteins; D002118:Calcium