The effects of truncations of the small subunit on m-calpain activity and heterodimer formation

TY - JOUR

T1 - The effects of truncations of the small subunit on m-calpain activity and heterodimer formation

AU - Elce, John S.

AU - Davies, Peter L.

AU - Hegadorn, Carol

AU - Maurice, Donald H.

AU - Arthur, J. Simon C.

PY - 1997/8/15

Y1 - 1997/8/15

N2 - In order to study subunit interactions in calpain, the effects of small subunit truncations on m-calpain activity and heterodimer formation have been measured. It has been shown previously that active calpain is formed by co-expression of the large subunit (80 kDa) of rat m-calpain with a δ86 form (21 kDa) of the small subunit. cDNA for the full-length 270 amino acid (28.5 kDa) rat calpain small subunit has now been cloned, both with and without an N-terminal histidine tag (NHis10). The full-length small subunit constructs yielded active calpains on co-expression with the large subunit, and the small subunit was autolysed to 20 kDa on exposure of these calpains to Ca2+. A series of deletion mutants of the small subunit, NHis10-δ86. δ99, -δ107, and -δ116, gave active heterodimeric calpains with unchanged specific activities, although in decreasing yield, and with a progressive decrease in stability. NHis10-δ125 formed a heterodimer which was inactive and unstable. Removal of 25 C-terminal residues from Δ86, leaving residues 87-245, abolished both activity and heterodimer formation. The results show that: (a) generation of active m-calpain in Escherichia coli requires heterodimer formation; (b) small subunit residues between 94 and 116 contribute to the stability of the active heterodimer but do not directly affect the catalytic mechanism; (c) residues in the region 245-270 are essential for subunit binding. Finally, it was shown that an inactive mutant Cys105→Ser-80k/δ86 calpain, used in order to preclude autolysis, did not dissociate in the presence of Ca2+, a result which does not support the proposal that Ca2+-induced dissociation is involved in calpain activation.

AB - In order to study subunit interactions in calpain, the effects of small subunit truncations on m-calpain activity and heterodimer formation have been measured. It has been shown previously that active calpain is formed by co-expression of the large subunit (80 kDa) of rat m-calpain with a δ86 form (21 kDa) of the small subunit. cDNA for the full-length 270 amino acid (28.5 kDa) rat calpain small subunit has now been cloned, both with and without an N-terminal histidine tag (NHis10). The full-length small subunit constructs yielded active calpains on co-expression with the large subunit, and the small subunit was autolysed to 20 kDa on exposure of these calpains to Ca2+. A series of deletion mutants of the small subunit, NHis10-δ86. δ99, -δ107, and -δ116, gave active heterodimeric calpains with unchanged specific activities, although in decreasing yield, and with a progressive decrease in stability. NHis10-δ125 formed a heterodimer which was inactive and unstable. Removal of 25 C-terminal residues from Δ86, leaving residues 87-245, abolished both activity and heterodimer formation. The results show that: (a) generation of active m-calpain in Escherichia coli requires heterodimer formation; (b) small subunit residues between 94 and 116 contribute to the stability of the active heterodimer but do not directly affect the catalytic mechanism; (c) residues in the region 245-270 are essential for subunit binding. Finally, it was shown that an inactive mutant Cys105→Ser-80k/δ86 calpain, used in order to preclude autolysis, did not dissociate in the presence of Ca2+, a result which does not support the proposal that Ca2+-induced dissociation is involved in calpain activation.

UR - https://www.scopus.com/pages/publications/0030883152

U2 - 10.1042/bj3260031

DO - 10.1042/bj3260031

M3 - Article

C2 - 9337847

AN - SCOPUS:0030883152

SN - 0264-6021

VL - 326

SP - 31

EP - 38

JO - Biochemical Journal

JF - Biochemical Journal

IS - 1

ER -