Mannose-6-phosphate targets proteins to the endoplasmic reticulum

Question

BlackTom AI · Accepted Answer

The statement to evaluate is: 'Mannose-6-phosphate targets proteins to the endoplasmic reticulum'.

First, consider what Mannose-6-phosphate (M6P) actually does in the cell. M6P is a tag added to certain lysosomal hydrolases in the Golgi apparatus, not in the endoplasmic reticulum. This modification serves as a signal for proper trafficking of these enzymes to the lysosome.

Next, examine the pathway involved: after hydrolases acquire the M6P tag in the Golgi, they are recognized by M6P receptors in the trans-Golgi network, packaged into clathrin-coated vesicles, and delivered to late endosomes and lysosomes. This pathway is specifically lysosomal targeting, not delivery to the ER.

Contrast this with how proteins are directed to the endoplasmic reticulum. ER targeting relies primarily on an N-terminal signal peptide that directs ribosome-associated translation to the ER membrane, and retention within the ER often involves signals such as the KDEL sequence for soluble resident proteins. There is no role for M6P in this ER targeting or retention process.

Therefore, the claim that Mannose-6-phosphate targets proteins to the endoplasmic reticulum misstates the trafficking route. The M6P signal is a lysosomal targeting tag, not an ER localization signal.

In summary, the reasoning behind why this statement is incorrect centers on the distinct trafficking roles: M6P marks lysosomal enzymes for delivery to lysosomes, while ER targeting relies on signal peptides and retention signals unrelated to M6P.

Mannose-6-phosphate targets proteins to the endoplasmic reticulum判断题

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