P-domain and lectin site are involved in the chaperone function of Saccharomyces cerevisiae calnexin homologue.

Cne1p, a calnexin homologue from Saccharomyces cerevisiae, has been shown to possess a conserved P-domain and lectin site as mammalian calnexin. The effect of P-domain and lectin site on the function of Cne1p was investigated in vitro using recombinant P-domain, P-domain deletion mutant of Cne1p, and lectin site mutant of Cne1ps (E181A and E398A) The binding of monoglucosylated oligosaccharide (G1M9) with Cne1p was clearly demonstrated using lectin site mutants. The P-domain deletion mutant and the letcin site mutants partially decreased the ability to suppress the aggregation of citrate synthase (CS) and chicken egg yolk immunoglobulin at levels different from Cne1p. Furthermore, the P-domain deletion mutant and the lectin site mutants decreased the ability to enhance the refolding of CS. These results suggest that the cooperation between the P-domain and the lectin site are important for the complete function of Cne1p. Thus, we conclude that P-domain in cooperation with the lectin site of Cne1p functions as a chaperone.