Fig. 1.

Subunit composition, membrane topology and domain organization of the STT3A and STT3B complexes. Multisubunit OSTs are composed of three subcomplexes. Proteins are shown using their mammalian names, with yeast protein names shown in parentheses. Yeast lack homologs of DC2 and KCP2. The C-terminal four-helix bundle of RPN1 and the N-terminal domain of RPN2 are not present in the yeast homologs (Ost1 and Swp1, respectively). NTD, MD and TRX designate N-terminal domains, middle domains and the thioredoxin domain, and are based upon the cryo-EM structure of the yeast OST (Bai et al. 2018; Wild et al. 2018) and the structures of OST6 and TUSC3 (Schulz et al. 2009; Mohorko et al. 2014). The diagrams for STT3A and STT3B depict the location of EL1, EL5 and a well-ordered N-glycan that is important for STT3 function.