Biogenesis, Structure and Function of Lysosomes
Published Online: 15 SEP 2006
Copyright © 2006 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.
Reviews in Cell Biology and Molecular Medicine
How to Cite
Dice, J. F. 2006. Biogenesis, Structure and Function of Lysosomes. Reviews in Cell Biology and Molecular Medicine. .
- Published Online: 15 SEP 2006
Lysosomes are organelles that are surrounded by a single membrane and contain many hydrolases that are most active at an acidic pH. The pH within the lysosomal lumen is usually maintained between 5.0 and 5.5 by a multisubunit, proton-pumping ATPase in the lysosomal membrane of mammalian cells and in the vacuolar membrane of yeast. Other organelles having some of the properties of lysosomes include late endosomes and multivesicular bodies. However, these organelles have protein and lipid constituents at least partially distinct from lysosomes.
Enzymes in the lysosomal lumen are targeted to that location by mannose 6-phosphate (M6P) carbohydrate modifications in the case of mammalian cell lysosomes or by linear peptide sequences for the yeast vacuole. Integral membrane proteins within the lysosomal and vacuolar membranes are targeted to that location due to critical tyrosine or dileucine peptide motifs in cytosolic regions of the proteins. These motifs interact with vesicle coat protein complexes that concentrate the proteins into vesicles destined for fusion with lysosomes. Peripheral lysosomal membrane proteins generally interact strongly with one or more integral membrane proteins and/or lipids.
Lysosomes account for 1 to 15% of cell volume and of cell protein in mammalian cells and 30 to 90% of cell volume in fungal and plant cells. This variability depends on cell type and physiological status. The morphological appearance of lysosomes also varies from vesicular to a more complex tubular lattice. Lysosomes are responsible for degrading both extracellular and intracellular proteins as well as other macromolecules.
The role of lysosomes in overall intracellular protein degradation depends on the cell type and nutritional conditions. Lysosomes are responsible for most protein degradation in liver and kidney, and certain lysosomal pathways of proteolysis are activated in response to nutritional deprivation. On the other hand, lysosomes play a minor role in protein degradation in skeletal muscle and lymphocytes, where the ubiquitin-proteasome proteolytic pathway predominates. Lysosomal pathways of proteolysis operate to some extent in all eukaryotic cells except in mature red blood cells that do not contain organelles, and there are at least six different pathways by which proteins can be delivered to lysosomes for digestion.
- Mannose 6-Phosphate Receptor;
- Lysosomal Storage Disease