Milner, M. T. | Search bioRxiv

bioRxiv2025

Caspase-1 self-terminates protease activity to enforce homeostasis and prevent inflammasome-driven diseases

Signal shutdown mechanisms must exist to silence the potent inflammatory programs initiated by the caspase-1 (CASP1) protease, to allow inflammation to resolve and reinstate tissue homeostasis. It is unknown how CASP1 terminates its activity in vivo. Here, we use a knock-in mouse model in which the CASP1 CARD domain linker (CDL) is mutated to prevent self-cleavage (Casp1.CDL mice) to show that CASP1 CDL autoproteolysis terminates CASP1 activity in vivo. We examined these mice under homeostatic conditions and in response to major physiological challenges. In the brain, CASP1 CDL mutation caused anxiety-like behaviour under homeostatic conditions, and exacerbated hippocampal spatial learning deficits in the APP23 genetic model of amyloid-induced neurodegeneration. In the bone marrow, CASP1 CDL mutation promoted steady-state granulopoiesis. In a model of diet-induced liver disease, CASP1 CDL mutation accelerated liver steatosis and promoted liver immune cell infiltration, inflammation and damage. In a liver healing model, CASP1 CDL mutation delayed disease resolution, indicating that CASP1 autocleavage is required to restore homeostasis after a major challenge to organ function. Our data reveal that CASP1 CDL self-cleavage terminates CASP1 inflammatory programs in vivo to maintain homeostasis in steady-state, restore homeostasis after a major challenge to organ function, and suppress inflammasome-driven diseases. These data identify CASP1 as a prime anti-inflammatory drug target, as CASP1 inhibitors may enforce homeostasis and prevent inflammasome-driven diseases.

immunology↗

bioRxiv2020

AscA (YecA) is a molecular chaperone involved in Sec-dependent protein translocation in Escherichia coli

Proteins that are translocated across the cytoplasmic membrane by Sec machinery must be in an unfolded conformation in order to pass through the protein-conducting channel during translocation. Molecular chaperones assist Sec-dependent protein translocation by holding substrate proteins in an unfolded conformation in the cytoplasm until they can be delivered to the membrane-embedded Sec machinery. For example, in Escherichia coli, SecB binds to a subset of unfolded Sec substrates and delivers them to the Sec machinery by interacting with the metal-binding domain (MBD) of SecA, an ATPase required for translocation in bacteria. Here, we describe a novel molecular chaperone involved Sec-dependent protein translocation, which we have named AscA (for accessory Sec component). AscA contains a metal-binding domain (MBD) that is nearly identical to the MBD of SecA. In vitro binding studies indicated that AscA binds to SecB and ribosomes in an MBD-dependent fashion. Saturated transposon mutagenesis and genetics studies suggested that AscA is involved in cell-envelope biogenesis and that its function overlaps with that of SecB. In support of this idea, AscA copurified with a range of proteins and prevented the aggregation of citrate synthase in vitro. Our results suggest that AscA is molecular chaperone and that it enhances Sec-dependent protein translocation by delivering its substrate proteins to SecB. IMPORTANCEThis research describes the discovery of a novel molecular chaperone, AscA (YecA). The function of AscA was previously unknown. However, it contains a small domain, known as the MBD, suggesting it could interact with the bacterial Sec machinery, which is responsible for transporting proteins across the cytoplasmic membrane. The work described this study indicates that the MBD allows AscA to bind to both the protein synthesis machinery and the Sec machinery. The previously function of the previously uncharacterised N-terminal domain is that of a molecular chaperone, which binds to unfolded substrate proteins. We propose that AscA binds to protein substrates as they are still be synthesised by ribosomes in order to channel them into the Sec pathway.

molecular biology↗