Abstract
A key prerequisite of transporter proteins' function is their trafficking to the target cellular membranes where they fulfill distinct physiological roles. Cornichon proteins (CNIH/Erv14) represent a highly conserved family of coat protein complex II (COPII)-coated vesicle cargo receptors that facilitate the exit of numerous transporters from the endoplasmic reticulum (ER) to proceed via the secretory pathway. Despite their biomedical significance, the cargo specificities of the four human cornichons (CNIH1-4) remain largely unexplored. Here, we conducted a bioinformatics analysis of the CNIH/Erv14 family, revealing evolutionary conservation profiles of the family based on an alignment of 1879 sequences. AlphaFold3 modeling predicts that residues identified as the most evolutionarily conserved in cornichon family interact with Sec24 proteins of COPII vesicles. We also demonstrate the suitability of the model yeast Saccharomyces cerevisiae for studying the properties and putative interactors of human cornichons. We engineered S. cerevisiae strains in which the endogenous cornichon gene (ERV14) was replaced with human CNIH1, CNIH2, or CNIH4 coding sequences or CNIH coding sequences were expressed from multi-copy plasmids. The studied human cornichons were functional in S. cerevisiae cells and, to varying extents, complemented the differing phenotypes related to yeast ScErv14 roles in monovalent-cation homeostasis. The presence of human CNIHs supported the functioning of the yeast plasma-membrane Na(+), K(+)/H(+) antiporter Nha1, a known cargo of ScErv14. Both yeast ScErv14 and human CNIH cornichons improved the plasma-membrane targeting and functioning of the human Na(+)/H(+) antiporter NHA2 in yeast cells, identifying NHA2 as a novel cargo of cornichon COPII cargo receptors.