title: Structural basis for executioner caspase recognition of P5 position in substrates.
abstract: Caspase-3, -6 and -7 cleave many proteins at specific sites to induce apoptosis. Their recognition of the P5 position in substrates has been investigated by kinetics, modeling and crystallography. Caspase-3 and -6 recognize P5 in pentapeptides as shown by enzyme activity data and interactions observed in the crystal structure of caspase-3/LDESD and in a model for caspase-6. In caspase-3 the P5 main-chain was anchored by interactions with Ser209 in loop-3 and the P5 Leu side-chain interacted with Phe250 and Phe252 in loop-4 consistent with 50% increased hydrolysis of LDEVD relative to DEVD. Caspase-6 formed similar interactions and showed a preference for polar P5 in QDEVD likely due to interactions with polar Lys265 and hydrophobic Phe263 in loop-4. Caspase-7 exhibited no preference for P5 residue in agreement with the absence of P5 interactions in the caspase-7/LDESD crystal structure. Initiator caspase-8, with Pro in the P5-anchoring position and no loop-4, had only 20% activity on tested pentapeptides relative to DEVD. Therefore, caspases-3 and -6 bind P5 using critical loop-3 anchoring Ser/Thr and loop-4 side-chain interactions, while caspase-7 and -8 lack P5-binding residues.
authors.affiliation: Department of Biology, Molecular Basis of Disease Program, Georgia State University, Atlanta, GA 30303, USA.
authors.forename: Guoxing
authors.initials: G
authors.lastname: Fu
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Chumanevich
authors.forename: Johnson
authors.initials: J
authors.lastname: Agniswamy
authors.forename: Bin
authors.initials: B
authors.lastname: Fang
authors.forename: Robert W
authors.initials: RW
authors.lastname: Harrison
authors.forename: Irene T
authors.initials: IT
authors.lastname: Weber
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis; D053148:Caspase 3 / Q000737:chemistry; D053178:Caspase 6 / Q000737:chemistry; D053179:Caspase 7 / Q000737:chemistry; D053181:Caspase 8 / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray / Q000379:methods; D003546:Cysteine Endopeptidases / Q000737:chemistry*; D006801:Humans; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D010455:Peptides; D053148:Caspase 3; D053178:Caspase 6; D053179:Caspase 7; D053181:Caspase 8; D003546:Cysteine Endopeptidases
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