Identification of an ERGIC ‐Like Compartment in Fission Yeast: Emp43 Functions as a Lectin‐Like Cargo Receptor for Glycosylated Proteins

The endoplasmic reticulum‐Golgi intermediate compartment (ERGIC) plays a crucial role in the secretory pathway; however, its existence and function in lower eukaryotes remain largely unexamined. In this study, we identified Emp43 (SPBC4F6.05c) of Schizosaccharomyces pombe , an orthologue of human ( Homo sapiens ) ERGIC‐53, and demonstrated its localization to an ERGIC‐like compartment. The localization of Emp43 depended on its C‐terminal KYL motif and oligomerization through the CC1 domain. Deletion of S. pombe emp43 + resulted in significant sensitivity to MgCl 2 and FK506, along with defects in septum integrity, indicating a role in cell wall maintenance. Further analysis identified Ssp120 of S. pombe , an orthologue of human MCFD2, as a functional partner of Emp43. Yeast two‐hybrid assays confirmed a strong interaction between Emp43 and Ssp120, and both proteins co‐localized within an ERGIC‐like compartment. Additionally, we identified Meu17 of S. pombe , a glucan‐α‐1,4‐glucosidase homolog, as a potential ligand for Emp43. Overexpression of Meu17 rescued MgCl 2 sensitivity in both emp43 Δ and ssp120 Δ strains, while mutations in its N‐linked glycosylation sites (N383, N409) or its predicted active site (D203) disrupted its septum localization and functional rescue capability. Our findings indicate that Emp43 forms a complex with Ssp120 to facilitate the transport of glycosylated proteins, such as Meu17, within an ERGIC‐like compartment in fission yeast S. pombe . This study provides the first evidence of an ERGIC‐like structure in S. pombe and highlights the conserved nature of ERGIC‐associated mechanisms across eukaryotes.