In addition, this selectivity permits CMA to play a regulatory role in multiple cellular processes by contributing to modulate intracellular levels of enzymes, transcription factors and cell maintenance proteins 4. This allows for the removal of specific proteins without disturbance of neighboring ones and makes CMA an efficient system for degradation of damaged or abnormal proteins, and surplus subunits of multi-protein complexes. One of the distinctive features of CMA is that proteins that undergo degradation by this autophagic pathway are selected individually through a recognition motif in their amino acid sequences 5. This process is known as chaperone-mediated autophagy (CMA) and constitutes the focus of this review 4. Proteins can be targeted from the cytosol to the lysosomal membrane and then gain access to the lumen of this organelle by directly crossing its membrane. However, not all lysosomal delivery involves vesicles. These vesicles then pinch off into the lysosomal lumen and are degraded by the proteases inside lysosomes. In other cases, such as microautophagy, proteins are trapped inside vesicles that form directly through the invagination of the lysosomal membrane. In some instances, such as macroautophagy, proteins are sequestered in vesicles that form in the cytosol and then fuse with lysosomes to transfer their contents for degradation. Delivery of proteins to lysosomes for degradation, or autophagy, can occur through different mechanisms 3. Proteins can undergo degradation by the proteasome or by lysosomes. This constant renewal of the proteome assures its proper functioning and permits a tight control of intracellular levels of proteins as a way to modulate multiple intracellular processes 1, 2. Intracellular proteins are subjected to continuous turn-over through coordinated synthesis, degradation and recycling of their component amino acids.
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