| Adaptor proteins act as a bridge between clathrin and membrane lipids during clathrin-mediated budding processes in all cells. UNC-11 is the C. elegans homologue of AP180, a monomeric clathrin adaptor protein enriched in neurons. The unc-11 gene encodes at least 6 protein isoforms. Isoforms A, C and E have been tested for function in vivo and all can rescue the unc-11 null mutant phenotype. Sixteen independently isolated mutant alleles were characterized and all have mutations in the first shared five exons.; The N-terminal region of the UNC-11 protein defines a protein-lipid interaction domain, the ANTH domain and a putative PI(4,5)P2 binding motif resides in this domain. The ANTH domain containing proteins, in contrast to full length UNC-11 proteins, are retained in the cell bodies of neurons. Full-length UNC-11 proteins and wild type ANTH domain containing proteins are highly enriched on the plasma membrane, whereas proteins containing a mutant ANTH domain are homogenously distributed in the neuronal cells and display a distribution like non-functional proteins.; Two full-length proteins lacking the PIP binding motif were tested for in vivo function and neither protein was recruited to the plasma membrane even though they were transported to the synaptic terminals. These mutant proteins can partially rescue the behavioral defects of unc-11 null mutants and can properly traffic synaptobrevin.; My observations suggest that the ANTH domain is important for targeting the proteins to the plasma membrane and the PIP binding motif is necessary for the targeting. These studies support two conclusions. First, PI(4,5)P 2 is one but not the sole ligand recruiting UNC-11 proteins to specific sites on the plasma membrane. Second, the C-terminal region of UNC-11 protein is necessary for the transport of UNC-11 proteins to the synaptic terminals. |
