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Srimathi T , Robbins SL , Dubas RL , Chang H , Cheng H , Roder H , Park YC
Mapping of POP1-binding site on pyrin domain of ASC
J Biol Chem. 2008 May 30;283(22) :15390-8
PMID: 18362139   
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Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is an essential adaptor protein in the formation of a multiprotein complex that activates procaspase-1. ASC is also known as a modulator of NF-kappaB activation pathways. ASC has a bipartite domain structure, consisting of an N-terminal pyrin domain (PYD) and a C-terminal caspase-recruitment domain. The PYD of ASC (ASC_PYD) is known to interact with various PYD-containing intracellular danger signal sensors and PYD-only proteins. Using purified proteins, we characterized the in vitro interaction of ASC_PYD with PYD-only protein 1 (POP1). POP1 specifically interacts with ASC_PYD with a dissociation constant of 4.08 +/- 0.52 microm but does not interact with Cryopyrin. NMR and mutagenesis experiments show that a negative electrostatic potential surface patch (EPSP) on ASC_PYD, consisting of the first (H1) and fourth (H4) helices, is essential in the interaction with POP1. A positive EPSP on POP1, consisting of the second (H2) and third (H3) helices, is a counterpart of this interaction. The interaction between ASC_PYD and POP1 is similar to the interaction between caspase recruitment domains of Apaf-1 and procaspase-9. In addition, we present evidence that conformational changes at the long loop of ASC_PYD between the H2 and H3 helices can affect its interaction with POP1. Based on our observations, we propose that the positive EPSP of ASC_PYD, including the H2 and H3 helices, may be the binding site for Cryopyrin, and the interaction with Cryopyrin may induce the dissociation of POP1 from ASC_PYD.
Srimathi, Thiagarajan Robbins, Sheila L Dubas, Rachel L Chang, Helen Cheng, Hong Roder, Heinrich Park, Young Chul Research Support, Non-U.S. Gov't United States The Journal of biological chemistry J Biol Chem. 2008 May 30;283(22):15390-8. Epub 2008 Mar 24.