253-LB: A Novel Membrane Binding Domain in Conjunction with Golga5 Recruits the Secretory Granule Biogenesis Factor HID-1 to the Golgi

Secretory granules (SGs) mediate the regulated release of neuropeptides and peptide hormones. HID-1 is a TGN localized peripheral membrane protein contributing to SG formation. Mice lacking HID-1 specifically in pancreatic β-cells are glucose intolerant and display impaired insulin secretion. However, there is no information about the structure or domain architecture of HID-1, and thus it remains unknown how HID-1 binds to the TGN and performs its function. We report that the N-terminus of HID-1 mediates membrane binding through a myristoyl group with a polybasic amino acid patch but lacks specificity for the TGN. Delineation of the minimal domain responsible for HID-1 targeting to the TGN reveals an interaction with the Golgi-localized protein Golga5. Finally, we identify the C-terminus as a novel membrane binding region and the functional domain of HID-1. This isolated domain, when tethered to the TGN, is also capable of rescuing the secretion and sorting defects observed in HID-1 KO cells. Finally, a point mutation within that domain, identified in patients with endocrine and neurological deficits, is not functional. We propose that HID-1 N-terminal and C-terminal domains, in cooperation with Golga5, ensure specific binding to Golgi membranes and functionality of HID-1.