Self-oligomerization of ASC PYD Domain Prevents the Assembly of Inflammasome In Vitro

NALP3 inflammasome, which is an inflammatory caspase-activating complex, is composed of three proteins: NALP3 (an NOD-like receptor), an apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and caspase-1. NALP3 senses danger signals, while ASC is an adaptor molecule containing two protein interaction modules: pyrin domain (PYD) and caspase recruitment domain (CARD). Caspase-1 is a cysteine protease that uses cysteine as a nucleophile and has a CARD domain for protein interaction. During inflammasome formation, the ASC adaptor acts as a bridge between caspase and NOD-like receptor (NLR) by offering the CARD for CARD–CARD interactions and PYD for PYD–PYD interactions. In the current study, we successfully purified and characterized NALP3 PYD and ASC PYD. The results showed that ASC PYD easily self-oligomerized under physiological conditions, and this self-oligomerization of the ASC PYD prevented complex formation with NALP3 PYD in vitro.