title: Phosphorylation regulates assembly of the caspase-6 substrate-binding groove.
abstract: Caspases, a family of apoptotic proteases, are increasingly recognized as being extensively phosphorylated, usually leading to inactivation. To date, no structural mechanism for phosphorylation-based caspase inactivation is available, although this information may be key to achieving caspase-specific inhibition. Caspase-6 has recently been implicated in neurodegenerative conditions including Huntington's and Alzheimer's diseases. A full understanding of caspase-6 regulation is crucial to caspase-6-specific inhibition. Caspase-6 is phosphorylated by ARK5 kinase at serine 257 leading to suppression of cell death via caspase-6 inhibition. Our structure of the fully inactive phosphomimetic S257D reveals that phosphorylation results in a steric clash with P201 in the L2' loop. Removal of the proline side chain alleviates the clash resulting in nearly wild-type activity levels. This phosphomimetic-mediated steric clash causes misalignment of the substrate-binding groove, preventing substrate binding. Substrate-binding loop misalignment appears to be a widely used regulatory strategy among caspases and may present a new paradigm for caspase-specific control.
authors.affiliation: Department of Chemistry, University of Massachusetts Amherst, Amherst, MA 01003, USA.
authors.forename: Elih M
authors.initials: EM
authors.lastname: Velázquez-Delgado
authors.forename: Jeanne A
authors.initials: JA
authors.lastname: Hardy
mesh_terms: D017209:Apoptosis / Q000235:genetics; D001665:Binding Sites; D053178:Caspase 6 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli; D006801:Humans; D008958:Models, Molecular; D018716:Molecular Mimicry; D019636:Neurodegenerative Diseases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011392:Proline / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000737:chemistry* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D012097:Repressor Proteins; D012694:Serine; D011392:Proline; D011494:Protein Kinases; C470845:NUAK1 protein, human; D053178:Caspase 6