The CRD domain of LMAN1 is responsible for MCFD2 binding in vivo. (A) Diagram of LMAN1 mutants used in the experiments. SS, signal peptide; F, Flag; TM, transmembrane. KKFF represents the last 4 amino acids of wild-type LMAN1 important for ER exit and retrieval, while KKAA represents mutations of the last 2 amino acids. (B) Co-IP of LMAN1 mutants with MCFD2. COS1 cells were cotransfected with Flag-tagged LMAN1 mutants and myc-tagged wild-type MCFD2. Cell lysates were immunoprecipitated with anti-myc for MCFD2 and anti-Flag for LMAN1.