In silico screening for palmitoyl substrates reveals a role for DHHC1/3/10 (zDHHC1/3/11)-mediated neurochondrin palmitoylation in its targeting to Rab5-positive endosomes.

Protein palmitoylation, a common post-translational lipid modification, plays an important role in protein trafficking and functions. Recently developed palmitoyl-proteomic methods identified many novel substrates. However, the whole picture of palmitoyl substrates has not been clarified. Here, we performed global in silico screening using the CSS-Palm 2.0 program, free software for prediction of palmitoylation sites, and selected 17 candidates as novel palmitoyl substrates. Of the 17 candidates, 10 proteins, including 6 synaptic proteins (Syd-1, transmembrane AMPA receptor regulatory protein γ-2, γ-8, cornichon-2, Ca(2+)/calmodulin-dependent protein kinase IIα, and neurochondrin (Ncdn)/norbin), one focal adhesion protein (zyxin), two ion channels (TRPM8 and TRPC1), and one G-protein-coupled receptor (orexin 2 receptor), were palmitoylated. Using the DHHC palmitoylating enzyme library, we found that all tested substrates were palmitoylated by the Golgi-localized DHHC3/7 subfamily. Ncdn, a regulator for neurite outgrowth and synaptic plasticity, was robustly palmitoylated by the DHHC1/10 (zDHHC1/11; z1/11) subfamily, whose substrate has not yet been reported. As predicted by CSS-Palm 2.0, Cys-3 and Cys-4 are the palmitoylation sites for Ncdn. Ncdn was specifically localized in somato-dendritic regions, not in the axon of rat cultured neurons. Stimulated emission depletion microscopy revealed that Ncdn was localized to Rab5-positive early endosomes in a palmitoylation-dependent manner, where DHHC1/10 (z1/11) were also distributed. Knockdown of DHHC1, -3, or -10 (z11) resulted in the loss of Ncdn from Rab5-positive endosomes. Thus, through in silico screening, we demonstrate that Ncdn and the DHHC1/10 (z1/11) and DHHC3/7 subfamilies are novel palmitoyl substrate-enzyme pairs and that Ncdn palmitoylation plays an essential role in its specific endosomal targeting.

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