Abstract 15853: Identification of Novel Sites Required for PCSK9 Autocatalytic Cleavage

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that promotes degradation of cell surface LDL receptors (LDLRs). Decrease in circulating PCSK9 levels by monoclonal antibodies is correlated with improved lipid profiles in humans. In contrast to therapeutic antibodies, strategies to inhibit PCSK9 with a small molecule have proven to be challenging. Here we explored a potential strategy to decrease PCSK9 level by inhibiting its autocatalytic cleavage and subsequent secretion. We discovered a tool compound, which represents a highly reactive lactone series irreversible inhibitors, that can non-specifically bind to multiple sites on PCSK9 and prevent its autocatalytic cleavage and secretion. Mass spectrometry studies confirmed that serine residues 326 (S326) and 329 (S329) are the main binding sites. Structurally, S326 and S329 are far away from the PCSK9 autocatalytic cleavage site serine 386 (S386). Mutagenesis of S326/S329 reduced PCSK9 autocatalytic cleavage intracellularly. Thr...