Which of the following signals directs a protein to the lysosomes?
I-cell disease A lysosomal storage disorder characterized by the accumulation of materials which would usually be broken down in lysosomes. This is found to be because lysosomal enzymes are not being directed to the lysosomes. When the lysosomal enzymes are examined it is found that their protein structure is normal, but the carbohydrate chains attached to the enzymes terminate with a mannose, whereas in normal lysosomal enzymes the carbohydrates terminate with mannose-6-phosphate. Thus, it seems that the terminal mannose-6-phosphate constitutes the signal which directs proteins to the lysosomes. When the mannose is not phosphorylated, the enzymes are directed to secretory vesicles instead. Reference: Harper; 30th edition
A lys-asp-glu- leu (KDEL) sequence in the protein
Dolichol phosphate
Attached carbohydrate with terminal mannose-6-phosphate
Attached carbohydrate with terminal mannose
Structure and function of protein