Analysis of the maturation of the ER‐Degradation Enhancing α‐Mannosidase like protein (EDEM)

Abstract

The ER quality control system targets misfolded proteins for degradation through the ER-associated degradation (ERAD) process. EDEM, a putative Type II membrane protein is proposed to extract aberrant glycoproteins from the calnexin cycle by recognizing specific glycoforms. To provide a more complete understanding of EDEMs role in protein degradation, we have analyzed the maturation of EDEM within the ER. EDEM is initially synthesized as a type II membrane protein possessing four or five N-linked glycans. At steady-state in mammalian cells, EDEM also exists as a cleaved soluble protein with four or five glycans. These results indicate that EDEM is post-translationally cleaved, removing its N-terminal signal anchor sequence to produce the soluble form. Both soluble and membrane-bound forms of EDEM were found in dense membrane fractions that co-localize with ER and lysosomal markers by equilibrium density centrifugation. Together, these results indicate the differential maturation of EDEM contributes to its varying topologies and glycosylation states. This work is supported by Public Health Service Grant CA79864.