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Molecular basis of caspase-1 polymerization and its inhibition by a new capping mechanism.

ABSTRACT: Inflammasomes are cytosolic caspase-1-activation complexes that sense intrinsic and extrinsic danger signals, and trigger inflammatory responses and pyroptotic cell death. Homotypic interactions among Pyrin domains and caspase recruitment domains (CARDs) in inflammasome-complex components mediate oligomerization into filamentous assemblies. Several cytosolic proteins consisting of only interaction domains exert inhibitory effects on inflammasome assembly. In this study, we determined the structure of the human caspase-1 CARD domain (caspase-1(CARD)) filament by cryo-electron microscopy and investigated the biophysical properties of two caspase-1-like CARD-only proteins: human inhibitor of CARD (INCA or CARD17) and ICEBERG (CARD18). Our results reveal that INCA caps caspase-1 filaments, thereby exerting potent inhibition with low-nanomolar Ki on caspase-1(CARD) polymerization in vitro and inflammasome activation in cells. Whereas caspase-1(CARD) uses six complementary surfaces of three types for filament assembly, INCA is defective in two of the six interfaces and thus terminates the caspase-1 filament.

SUBMITTER: Lu A

PROVIDER: S-EPMC4856535 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Molecular basis of caspase-1 polymerization and its inhibition by a new capping mechanism.

Lu Alvin A Li Yang Y Schmidt Florian I FI Yin Qian Q Chen Shuobing S Fu Tian-Min TM Tong Alexander B AB Ploegh Hidde L HL Mao Youdong Y Wu Hao H

Nature structural & molecular biology 20160404 5

Inflammasomes are cytosolic caspase-1-activation complexes that sense intrinsic and extrinsic danger signals, and trigger inflammatory responses and pyroptotic cell death. Homotypic interactions among Pyrin domains and caspase recruitment domains (CARDs) in inflammasome-complex components mediate oligomerization into filamentous assemblies. Several cytosolic proteins consisting of only interaction domains exert inhibitory effects on inflammasome assembly. In this study, we determined the structu ...[more]

PMID: 27043298

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Project description:S-Crystallin from octopus lens has a tertiary structure similar to sigma-class glutathione transferase (GST). However, after isolation from the lenses, S-crystallin was found to aggregate more easily than sigma-GST. In vitro experiments showed that the lens S-crystallin can be polymerized and finally denatured at increasing concentration of urea or guanidinium chloride (GdmCl). In the intermediate concentrations of urea or GdmCl, the polymerized form of S-crystallin is aggregated, as manifested by the increase in light scattering and precipitation of the protein. There is a delay time for the initiation of polymerization. Both the delay time and rate of polymerization depend on the protein concentration. The native protein showed a maximum fluorescence emission spectrum at 341 nm. The GdmCl-denatured protein exhibited two fluorescence maxima at 310 nm and 358 nm, respectively, whereas the urea-denatured protein showed a fluorescence peak at 358 nm with a small peak at 310 nm. The fluorescence intensity was quenched. Monomers, dimers, trimers, and polymers of the native protein were observed by negative-stain electron microscopic analysis. The aggregated form, however, showed irregular structure. The aggregate was solubilized in high concentrations of urea or GdmCl. The redissolved denatured protein showed an identical fluorescence spectrum to the protein solution that was directly denatured with high concentrations of urea or GdmCl. The denatured protein was readily refolded to its native state by diluting with buffer solution. The fluorescence spectrum of the renatured protein solution was similar to that of the native form. The phase diagrams for the S-crystallin in urea and GdmCl were constructed. Both salt concentration and pH value of the solution affect the polymerization rate, suggesting the participation of ionic interactions in the polymerization. Comparison of the molecular models of the S-crystallin and sigma-GST suggests that an extra ion-pair between Asp-101 and Arg-14 in S-crystallin contributes to stabilizing the protomer. Furthermore, the molecular surface of S-crystallin has a protruding Lys-208 on one side and a complementary patch of aspartate residues (Asp-90, Asp-94, Asp-101, Asp-102, Asp-179, and Asp-180) on the other side. We propose a molecular model for the S-crystallin polymer in vivo, which involves side-by-side associations of Lys-208 from one protomer and the aspartate patch from another protomer that allows the formation of a polymeric structure spontaneously into a liquid crystal structure in the lens.

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Molecular basis of caspase-1 polymerization and its inhibition by a new capping mechanism.

Publications

Molecular basis of caspase-1 polymerization and its inhibition by a new capping mechanism.

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