title: Mechanism of Bcl-2 and Bcl-X(L) inhibition of NLRP1 inflammasome: loop domain-dependent suppression of ATP binding and oligomerization.
abstract: NLRP1 (NLR family, pyrin domain-containing 1) is a contributor to innate immunity involved in intracellular sensing of pathogens, as well as danger signals related to cell injury. NLRP1 is one of the core components of caspase-1-activating platforms termed "inflammasomes," which are involved in proteolytic processing of interleukin-1beta (IL-1beta) and in cell death. We previously discovered that anti-apoptotic proteins Bcl-2 and Bcl-X(L) bind to and inhibit NLRP1 in cells. Using an in vitro reconstituted system employing purified recombinant proteins, we studied the mechanism by which Bcl-2 and Bcl-X(L) inhibit NLRP1. Bcl-2 and Bcl-X(L) inhibited caspase-1 activation induced by NLRP1 in a concentration-dependent manner, with K(i) approximately 10 nM. Bcl-2 and Bcl-X(L) were also determined to inhibit ATP binding to NLRP1, which is required for oligomerization of NLRP1, and Bcl-X(L) was demonstrated to interfere with NLRP1 oligomerization. Deletion of the flexible loop regions of Bcl-2 and Bcl-X(L), which are located between the first and second alpha-helices of these anti-apoptotic proteins and which were previously shown to be required for binding NLRP1, abrogated ability to inhibit caspase-1 activation, ATP binding and oligomerization of NLRP1. Conversely, synthetic peptides corresponding to the loop region of Bcl-2 were sufficient to potently inhibit NLRP1. These findings thus demonstrate that the loop domain is necessary and sufficient to inhibit NLRP1, providing insights into the mechanism by which anti-apoptotic proteins Bcl-2 and Bcl-X(L) inhibit NLRP1.
authors.affiliation: Burnham Institute for Medical Research, La Jolla, CA 92037, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Faustin
authors.forename: Ya
authors.initials: Y
authors.lastname: Chen
authors.forename: Dayong
authors.initials: D
authors.lastname: Zhai
authors.forename: Gaelle
authors.initials: G
authors.lastname: Le Negrate
authors.forename: Lydia
authors.initials: L
authors.lastname: Lartigue
authors.forename: Arnold
authors.initials: A
authors.lastname: Satterthwait
authors.forename: John C
authors.initials: JC
authors.lastname: Reed
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism; D004789:Enzyme Activation; D007249:Inflammation / Q000378:metabolism*; D007700:Kinetics; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D051020:bcl-X Protein / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D010455:Peptides; D051020:bcl-X Protein; D000255:Adenosine Triphosphate; D020170:Caspase 1