What is the other name of lysosome


English: lysosome

1 definition

Lysosomes are cell organelles enclosed by a membrane in eukaryotes, which can be simply imagined as spherical vesicles. They contain hydrolytic enzymes and phosphatases with which they break down foreign substances or the body's own substances. Lysosomes are therefore also called Stomach of the cell designated.

2 structure

The lysosomes contain a wide variety of hydrolyzing enzymes such as proteases, nucleases and lipases for the intracellular digestion of material. These only achieve a high level of activity in an acidic environment. This ensures that enzymes that enter the cytosol from damaged lysosomes do not break down any important cellular components.

The interior (lumen) of lysosomes has a pH value below 5, which is actively maintained by a V-type ATPase. Under hydrolysis, it transports 2 protons from an ATP molecule into the lysosome. The membrane of the lysosomes has a specific protein structure. On the inside (E side), the membrane proteins are heavily glycosylated to protect against the enzymes.

3 protein transport to the lysosome

The lysosomal enzymes are synthesized in the endoplasmic reticulum (ER) during cotranslational protein transport and transferred into the ER lumen. They are then packed in transport vesicles and transported to the lysosomes via vesicular transport. In this way they also pass the Golgi apparatus. This organelle is used to decide whether a protein is secreted via the exocytosis or transported to other compartments.

Marking takes place in the Golgi apparatus so that lysosomal enzymes are packed into the correct vesicles. In the case of hydrolases, the marker is known: the carbohydrate mannose, which has already been bound to the proteins in the ER through N-glycosylation, is phosphorylated in the cis-Golgi apparatus. Two enzymes catalyze this modification: A phosphotransferase recognizes that it is a lysosomal enzyme and attaches N-acetylglucosamine-1-phosphate to one or two mannose residues. The second enzyme cuts off the N-acetylglucosamine residue, completing the labeling.

In the trans-Golgi apparatus, the mannose-6-phosphate groups (M6P groups) are finally recognized by M6P receptor proteins. The binding to these transmembrane proteins "sorts" the hydrolases into vesicles, which are then brought to the lysosomes.

4 secondary lysosomes

In the cytoplasm, the primary lysosomes fuse with endocytotic vesicles or phagosomes to form what are known as secondary lysosomes. One can distinguish several forms of secondary lysosomes:

In the heterolysosome, the M6P receptors separate from their ligands and are reused.

5 pathophysiology

A defect in the phosphotransferase leads to a so-called lysosomal storage disease. Since M6P cannot be labeled, the lysosomal enzymes are not sorted and get into the extracellular matrix in an uncontrolled manner (I-cell disease). Other lysosomal storage diseases are triggered by defects in lysosomal hydrolases. This leads to an increase in non-degraded material in the lysosomes. Most of the time, serious symptoms are the result.