FIGURE 30.1. Historical background regarding “cross-correction” of lysosomal enzyme deficiencies in cultured cells.

FIGURE 30.1

Historical background regarding “cross-correction” of lysosomal enzyme deficiencies in cultured cells. Small amounts of “high-uptake” lysosomal enzymes secreted by normal fibroblasts (thin arrows) were found to be taken up by fibroblasts from a patient with a genetic lack of a single lysosomal enzyme, correcting that deficiency. In contrast, I-cell disease fibroblasts secrete large amounts of multiple lysosomal enzymes of the “low-uptake“ variety (thick arrows). The latter forms cannot correct lysosomal enzyme deficiencies in other cells. However, I-cells retain the capability to accept “high-uptake” enzymes secreted by other cells (thin arrows). Uptake was blocked by the addition of mannose-6-phosphate (M6P) to the media. These data implied the existence of a “common recognition marker” that was missing on I-cells, and the existence of cell-surface receptors for the “high-uptake” forms. Subsequent studies showed that the recognition marker required mannose-6-phosphate on the N-glycans of the enzymes, and that the uptake was mediated by mannose-6-phophate receptors (MPRs).

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From: Chapter 30, P-type Lectins

Cover of Essentials of Glycobiology
Essentials of Glycobiology. 2nd edition.
Varki A, Cummings RD, Esko JD, et al., editors.
Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 2009.
Copyright © 2009, The Consortium of Glycobiology Editors, La Jolla, California.

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