In vitro proteolytic degradation of bovine brain calcineurin by m-calpain.
A major cause of neuronal dysfunction is due to altered Ca2+ regulation. An increase in Ca2+ influx can activate Ca2+-dependent enzymes including calpains, causing the proteolysis of its specific substrates. In the present study, calcineurin (CaN) was found to be proteolysed by a Ca2+-dependent cysteine protease, m-calpain. In the presence of Ca2+, the 60 kDa subunit (CaN A) was degraded to a 46 kDa immunoreactive fragment, whereas in the presence of Ca2+ /calmodulin (CaM) immunoreactive fragments of 48 and 54 kDa were observed. The beta-subunit (CaN B) was not proteolysed in either condition. The proteolysis of CaN A increased its phosphatase activity and rendered it totally CaM-independent after 10 min of proteolysis. The molecular weight of the proteolytic fragments suggested that the m-calpain cleaved CaN A in the CaN B binding domain. A CaM-overlay experiment revealed that the CaM-binding site was present only in the 54 kDa fragment produced by CaN A proteolysis in the presence of Ca2+ /CaM. Thus, the increase in CaN A phosphatase activity observed in many neuronal disorders, may be due to the action of calpain.
Lakshmikuttyamma
Ashakumary
A
Department of Pathology, College of Medicine, University of Saskatchewan, Saskatchewan Cancer Agency, Saskatoon, Saskatchewan, Canada S7N 4H4.
Selvakumar
Ponniah
P
Sharma
Anil Ratan
AR
Anderson
Deborah H
DH
Sharma
Rajendra K
RK
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism*; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism
D019703:Calcineurin; D010447:Peptide Hydrolases; D002154:Calpain; C449000:m-calpain