Patients with Hunter’s syndrome or with Hurler’s syndrome rarely live beyond the
ID: 204210 • Letter: P
Question
Patients with Hunter’s syndrome or with Hurler’s syndrome rarely live beyond their teens. These patients accumulate glycosaminoglycans in lysosomes due to the lack of specific lysosomal enzymes necessary for their degradation. When cells from patient with the two syndromes are fused, glycosaminoglycans are degraded properly, indicating that the cells are missing different degradative enzymes that complement with each other. Even if the cells are just cultured together, they still correct each other’s defects. Most surprising of all, the medium from a culture of Hurler’s cells corrects the defect in Hunter’s cells (and vice versa). The corrective factors in the media are inactivated by treatment with proteases, by treatment with periodate, which destroys carbohydrate, and by treatment with alkaline phosphatase, which removes phosphates. A. What do you suppose the corrective factors are? Beginning with the donor patients’ cells, describe the route by which the factors reach the medium and subsequently enter the recipient cells to correct the lysosomal defects? B. Why do you suppose the treatment with protease, periodate, and alkaline phosphatase inactivate the corrective factors? C. Would you expect a similar sort of correction scheme to work for mutant cytosolic enzymes?
Explanation / Answer
These corrective factors are vesicles. Enzymes in vesicles move out by exocytosis from the donors cell and enter the recipient by endocytosis. These first form endosomes then endolysosome and then fuse with existing lysosomes to replenish the enzymes.
B. Bother exocytosis and endocytosis require many proteins and enzymes for formation and as vesicles are basically part of cell membrane, periodate oxidizes the membrane of these vesicles.
C. Yes.