GPP130 stem region is necessary and sufficient for intra-Golgi cisternal rim localization of type II transmembrane proteins

Abstract

The Golgi complex is made up of cisternae stacks that are divided into multiple zones. Previous study from our lab showed that Golgi proteins partition to the interior or rim within the same cisterna, but the mechanisms for differential localization remains unknown. GPP130 and ST6GAL1 are type II transmembrane proteins that localize to the trans-Golgi. However, GPP130 is rim-localized, while ST6GAL1 is interior-localized. In this study, we attempt to find GPP130 domain that is responsible for intra-Golgi cisternal rim localization. To that end, we swapped domains between GPP130 and ST6GAL1 to make chimera proteins and performed super-resolution microscopy to study their cisternal localization. We demonstrated that the GPP130 stem region is necessary for the rim localization of the chimera proteins. Next, we fused GPP130 stem region with non-Golgi localized type II transmembrane proteins, TfR and TNF-α. We found that the GPP130 stem region was sufficient to localize TfR and TNF-α to the Golgi at the cisternal rim. Using Alphafold2, we found that the GPP130 stem region assembles a continuous and dimeric helical coiled-coil with the transmembrane domain. This could be a novel membrane curvature sensing module that brings GPP130 to the high curvature region of the Golgi cisternal rim.