Figure 1. Schematic model of proteasomal and autophagic degradation pathways in pro- and eukaryotes.

Figure 1

Schematic model of proteasomal and autophagic degradation pathways in pro- and eukaryotes. Proteins are degraded in prokaryotes by chambered proteases termed the 19S proteasome upon recognition of primary amino acid target sequences (red). The more complex 26S proteasome in eukaryotes is able to recognise and degrade polyubiquitinated (blue) proteins. a) Macroautophagy occurs by enveloping a part of the cytoplasm containing proteins and organelles in a cup shaped double isolation membrane (IM). The IM then closes resulting in the autophagosome (AP). The limiting membrane of the AP then fuses with the lysosome releasing the inner vesicle and its cargo for degradation. The two specific macroautophagic pathways, b) cytoplasm to vacuolar targeting (CVT) and c) macropexophagy occur in a similar manner. d) Microautophagy occurs by enveloping cytoplasm directly into the lysosome. Sometimes, direct uptake of organelles can occur such as during micropexophagy (d). While macroautophagy needs both Atg12 and Atg8 conjugation machineries, microautophagy appears to need only Atg8. e) The unrelated process of chaperone-mediated autophagy can transport proteins over the lysosomal membrane in an ATP-dependent manner. Ub-ubiquitin, 8-Atg8, 12-Atg12.

From: Origin and Evolution of Self-Consumption: Autophagy

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