The yeast kinase Yck2 tethers to the cytoplasmic surface of the plasma membrane through dual palmitoylation of its C-terminal Cys-Cys dipeptide, mediated by the Golgi-localized palmitoyl-transferase Akr1. Here, the Yck2 palmitoylation signal is found to consist of three parts: 1) a 10-residue-long, conserved C-terminal peptide (CCTP) that includes the C-terminal Cys-Cys dipeptide; 2) the kinase catalytic domain (KD); and mapping between these two elements; and 3) a 176-residue-long, poorly conserved, glutamine-rich sequence. The CCTP, which contains the C-terminal cysteines as well as an important Phe-Phe dipeptide, likely serves as an Akr1 recognition element, because CCTP mutations disrupt palmitoylation within a purified in vitro palmitoylation system. The KD contribution appears to be complex with roles for both KD activity (e.g., Yck2-mediated phosphorylation) and structure (e.g., Akr1 recognition elements). KD and CCTP mutations are strongly synergistic, suggesting that, like the CCTP, the KD may also participate at the Yck2-Akr1 recognition step. The long, glutamine-rich domain, which is located between the KD and CCTP, is predicted to be intrinsically disordered and may function as a flexible, interdomain linker, allowing a coupled interaction of the KD and CCTP with Akr1. Multipart palmitoylation signals may prove to be a general feature of this large class of palmitoylation substrates. These soluble proteins have no clear means of accessing membranes and thus may require active capture out of the cytoplasm for palmitoylation by their membrane-localized transferases.
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