A cell is unable to release certain proteins into the extracellular space. Which defect in GPI anchor processing could explain this?

• A. Defective ER retention signal, causing the protein to be retained in the ER.
• B. Failure to add the GPI anchor to the protein, preventing its attachment to the plasma membrane.
• C. Incorrect glycosylation of the protein, leading to misfolding.
• D. Inability to cleave the ER signal sequence, preventing protein translocation.

Answer: (B)