Inhibition of human initiator caspase 8 and effector caspase 3 by cross-class inhibitory bovSERPINA3-1 and A3-3

Serpins are a superfamily of structurally conserved proteins. Inhibitory serpins use a suicide substrate-like mechanism. Some are able to inhibit cysteine proteases in cross-class inhibition. Here, we demonstrate for the first time the strong inhibition of initiator and effector caspases 3 and 8 by two purified bovine SERPINA3s. SERPINA 3-1 (uniprotkb: Q9TTE1 ) binds tighly to human CASP3 (uniprotkb: P42574 ) and CASP8 (uniprotkb: Q14790 ) with kass of 4.2 × 105 and 1.4 × 106 M−1 s−1, respectively. A wholly similar inhibition of human CASP3 and CASP8 by SERPINA3-3 (uniprotkb: Q3ZEJ6 ) was also observed with kass of 1.5 × 105 and 2.7 × 106 M−1 s−1, respectively and form SDS-stable complexes with both caspases. By site-directed mutagenesis of bovSERPINA3-3, we identified Asp371 as the potential P1 residue for caspases. The ability of other members of this family to inhibit trypsin and caspases was analysed and discussed. Structured summary MINT- 7234656 : CASP8 (uniprotkb: Q14790 ) and SERPINA3-1 (uniprotkb: Q9TTE1 ) bind (MI: 0407 ) by biochemical (MI: 0401 ) MINT- 7234634 : SERPINA3-3 (uniprotkb: Q3ZEJ6 ) and CASP3 (uniprotkb: P42574 ) bind (MI: 0407 ) by biochemical (MI: 0401 ) MINT- 7234663 : CASP8 (uniprotkb: Q14790 ) and SERPINA3-3 (uniprotkb: Q3ZEJ6 ) bind (MI: 0407 ) by biochemical (MI: 0401 ) MINT- 7234625 : SERPINA3-1 (uniprotkb: Q9TTE1 ) and CASP3 (uniprotkb: P42574 ) bind (MI: 0407 ) by biochemical (MI: 0401 )