{'fraction_non_alphanumeric': 0.014705882352941176, 'fraction_numerical': 0.0, 'mean_word_length': 5.834061135371179, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Mosaic organization of the endocytic pathway.

In the era of genomic and proteomic research the biochemical composition of intracellular organelles becomes deciphered very rapidly. However, we still largely do not know how single components, proteins and lipids, are organized into higher order structures. By shifting the research focus toward the analysis of multicomponent complexes rather then individual molecules, it is becoming clear that proteins and lipids building organelle membranes are not evenly distributed throughout the bilayers but are able to segregate and form organized domains. Such compartmentalization ensures a high efficiency of various processes taking place simultaneously and warrants organelle integrity. Membrane domains can be considered modular building blocks and an organelle can be viewed as an unique and dynamic combination of various domains, coupled together spatially and functionally. Here we review some general mechanisms which are responsible for the formation of organized membrane domains. We provide examples of such structures present in the endocytic pathway, including lipid rafts, caveolae, and Rab-domains. Among molecules acting as domain organizers, we emphasize in particular the role of lipids, especially phosphoinositides, and Rab proteins. We further present a novel mechanism whereby different membrane domains can communicate between each other via divalent Rab effectors and discuss the implications of the domain concept for the structure–function relationship and biogenesis of endocytic organelles.