Identification of synaptic PPT1 substrates highlight roles of depalmitoylation in disulfide bond formation and synaptic function

Abstract

Loss-of-function mutations in the depalmitoylating enzyme palmitoyl protein thioesterase 1 (PPT1) cause Neuronal Ceroid Lipofuscinosis type 1 (CLN1), a devastating neurodegenerative disease. Here, we provide a resource identifying PPT1 substrates. We utilized Acyl Resin-Assisted Capture and mass spectrometry to identify proteins with increased in vivo palmitoylation in PPT1 knockout mouse brains. We then validated putative substrates through direct depalmitoylation with recombinant PPT1. This stringent screen elucidated >100 novel PPT1 substrates at the synapse, including channels and transporters, G-protein-associated molecules, endo/exocytic components, synaptic adhesion molecules, and mitochondrial proteins. Cysteine depalmitoylation sites in transmembrane PPT1 substrates frequently participate in disulfide bonds in the mature protein. We confirmed that depalmitoylation regulates disulfide bond formation in a tertiary screen analyzing post-translational modifications. Collectively, the diverse PPT1 substrates highlight the role of PPT1 in mediating synapse functions, implicate molecular pathways in the etiology of CLN1, and advance our basic understanding of the purpose of depalmitoylation. HighlightsO_LI[~]10% of palmitoylated proteins are palmitoyl protein thioesterase 1 (PPT1) substrates C_LIO_LIUnbiased proteomic approaches identify 9 distinct classes of PPT1 substrates, including synaptic adhesion molecules and endocytic proteins C_LIO_LIProtein degradation does not require depalmitoylation by PPT1 C_LIO_LIDepalmitoylation mediates disulfide bond formation in transmembrane PPT1 substrates C_LI