Although calnexin is essential in S-pombe, its highly conserved central domain is dispensable for viability

In mammalian cells, the calnexin/calreticulin chaperones play a key role in glycoprotein folding and its control within the endoplasmic reticulum (ER) , by interacting with folding intermediates via their monoglucosylated glyc ans, This lectin activity has been mapped in mammalian calnexin/calreticnli n chaperones to the central region, which is a highly conserved Feature of calnexin/calreticulin molecules across species. The central domain has also been implicated in Ca2+ binding, and it has been proposed to be involved i n the regulation of calcium homeostasis in the ER, Herein, we show that alt hough the Schizosaccharomyces pombe calnexin is essential for viability, ce lls lacking its 317-amino-acid highly conserved central region are viable u nder normal growth conditions. However, the central region appears to be ne cessary for optimal growth under high ER-stress, suggesting that this regio n is important under extreme folding situations (such as DTT and temperatur e). The minimal length of calnexin required for viability spans the C-termi nal 123 residues, Furthermore, cells with the central domain of the protein deleted were affected in their morphology at 37 degrees C, probably due to a defect in cell wall synthesis, although these mutant cells exhibited the same calcium tolerance as wild-type cells at 30 degrees C.