Regulation of clathrin adaptor protein complex‐1(AP‐1) by a Laa1 protein containing complex

The clathrin adaptor protein complex‐1 (AP‐1) is a critical regulator of membrane traffic at the trans‐ Golgi network. Its recruitment depends on the function of the small GTPase‐Arf1, phosphatidyl‐inositides, and members of the HEATR5 family, a poorly characterized family of proteins with members found in all eukaryotes. Although members of the HEATR5 family are known to be important for AP‐1 localization in diverse organisms, how they contributed to AP‐1 recruitment was unclear. We recently identified a conserved co‐factor for the yeast HEATR5 protein, Laa1, that acts as an AP‐1 binding cofactor. This co‐factor, Laa2, binds directly to AP‐1 and this interaction is required for AP‐1 localization, suggesting that direct interaction between the Laa1‐Laa2 protein complex and AP‐1 is essential for AP‐1 localization. Using proteomics and database mining, we have identified additional binding partners for Laa1. Phenotypic analysis suggests these binding partners are required for normal AP‐1 function, similar to Laa1 and Laa2. Here, we report the network of physical interactions between Laa1, Laa2, and two additional binding partners. Moreover, we find many of these proteins are unstable in the absence of their binding partners suggesting they may for a stable complex in vivo . These results suggest that a multi‐subunit complex centered on Laa1 controls AP‐1 functions. Support or Funding Information Protein Folding Disease Initiative at the University of Michigan NIGMS R01 GM129255