Differentielle, dynamische Syndapin-Komplexe als Modulatoren von Membrantopologie und -transport
Zusammenfassung der Projektergebnisse
Membrane topology modulation is an indispensable prerequisite for vesicle formation in membrane trafficking processes as well as for establishment, maintenance and plasticity of cellular morphology. It is catalyzed by the coordinated interplay of direct effectors that bend, tubulate and/or scission membranes and by organization and dynamics of the membrane-associated cortical cytoskeleton. BAR domain superfamily proteins, such as the F-BAR domain proteins of the syndapin family, have emerged as important components in membrane shaping. This project provided profound evidence that syndapins, which have the power to imprint their crescent shape onto membranes and furthermore recruit, coordinate and modulate the activity of cellular effectors, are indispensable for shaping cellular membranes and organelles and are critical for the development of cellular structures and whole organisms. Our studies revealed that the multifunctionality of syndapins is hereby based on their modular composition encompassing protein interaction modules as well as regions for lipid binding, dimerization and oligomerization. We furthermore showed that differentially regulated, dynamic syndapin complexes act as modulators of membrane topology and transport. The formation of syndapin oligomers hereby offers the possibility of syndapin-mediated physical interconnection of individual binder partners and their respective functions. Importantly, our studies indeed unveiled major interconnecting functions of multifunctional, differentially regulated, dynamic syndapin complexes particularly in neuromorphogenesis and revealed overlapping but also distinct properties of individual syndapin family members, further proteins of the F-BAR domain family as well as mechanistically somewhat related membrane shaping proteins of the reticulon family and finally a newly discovered and defined protein family, which we termed N-Ank proteins. For development of the signal-receiving, dendritic arbor of neurons, our results show that, surprisingly, the action of single actin filament-promoting factors was not sufficient for powering dendritogenesis. Instead, this process strictly required combining the functions of the actin nucleator Cobl and its only evolutionary distant ancestor Cobl-like acting interdependently. This coordination between Cobl-like and Cobl was achieved by physical linkage by the F-BAR protein syndapin I. Our work furthermore revealed that syndapin I formed nanodomains specifically at convex plasma membrane areas at the base of protrusive dendritic structures and interacted with three independent motifs in Cobl-like, one of which was Ca2+/calmodulin-regulated. Consistently, syndapin I, Cobl-like’s newly identified N terminal calmodulin-binding site and the single Ca2+/calmodulin-responsive syndapin binding motif all were absolutely critical for Cobl-like’s functions. In the development of the dendritic arbor, local Ca2+/CaM-controlled actin dynamics thus relies on regulated and physically coordinated interactions of different F-actin formation-promoting factors provided by syndapin proteins. The formation of caveolae, bulb-shaped plasma membrane invaginations, requires the coordinated action of distinct lipid-interacting and –shaping proteins. Several human diseases are associated with a lack of caveolae. The successful generation of knockout mice for the syndapin III isoform, which is highly expressed in heart and skeletal muscle, unveiled that muscle cells of syndapin III KO mice show severe reductions of caveolae reminiscent of human caveolinopathies. Yet the levels of plasma membrane-associated caveolar coat proteins were not reduced upon syndapin III KO. This allowed for dissecting bona fide caveolar functions from those supported by mere caveolin presence. Detailed studies demonstrated that syndapin III is crucial for caveolar invagination and that syndapin III KO rendered the cells sensitive to membrane tensions. Our analyses unveiled that in particular cellular integrity under strong mechanical stress was significantly affected in syndapin III KO muscles. Under physical exercise, failure to invaginate caveolae using the membraneshaping protein syndapin III coincided with a widened caliber spectrum, detached nuclei and signs of inflammation and necrosis. This pathophysiology in syndapin III KO muscles was reminiscent of human myopathies associated with CAVEOLIN3 mutation. These data highlight that syndapin III is crucial for caveolar invagination and that the physiological function of caveolin 3-coated caveolae is to preserve muscle cell integrity upon acute membrane tensions, as they occur during physical exercise and that this ability of muscular caveolae to respond to mechanical forces is a key physiological process.
Projektbezogene Publikationen (Auswahl)
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(2011). Let's go bananas: revisiting the endocytic BAR code. EMBO J 30, 3501-3515
Qualmann B, Koch D, Kessels MM
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(2011). The functions of the actin nucleator Cobl in cellular morphogenesis critically depend on syndapin I. EMBO J 30, 3147-3159
Schwintzer L, Koch N, Ahuja R, Grimm J, Kessels MM, Qualmann B
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(2012). Ultrastructural freeze-fracture immunolabeling identifies plasma membrane-localized syndapin II as a crucial factor in shaping caveolae. Histochem Cell Biol 138, 215-230
Koch D, Westermann M, Kessels MM, Qualmann B
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(2013). A spastic paraplegia mouse model reveals REEP1-dependent ER shaping. J Clin Invest 123, 4273-4282
Beetz C, Koch N, Khundadze M, Zimmer G, Nietzsche S, Hertel N, Huebner AK, Mumtaz R, Schweizer M, Dirren E, Karle KN, Irintchev A, Alvarez V, Redies C, Westermann M, Kurth I, Deufel T, Kessels MM, Qualmann B, Hübner CA
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(2013). Ciliated sensory hair cell formation and function require the F-BAR protein syndapin I and the WH2 domain-based actin nucleator Cobl. J Cell Sci 126, 196-208
Schüler S, Hauptmann J, Perner B, Kessels MM, Englert C, Qualmann B
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(2015). Regulation of endoplasmic reticulum turnover by selective autophagy. Nature 522, 354-358
Khaminets A, Heinrich T, Mari M, Grumati P, Huebner AK, Akutsu M, Liebmann L, Stolz A, Nietzsche S, Koch N, Mauthe M, Katona I, Qualmann B, Weis J, Reggiori F, Kurth I, Hübner CA, Dikic I
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(2017). Deciphering caveolar functions by syndapin III KO-mediated impairment of caveolar invagination. Elife 6, e29854
Seemann E, Sun M, Krueger S, Tröger J, Hou W, Haag N, Schüler S, Westermann M, Huebner CA, Romeike B, Kessels MM, Qualmann B
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(2019). Ankyrin repeat-containing N-Ank proteins shape cellular membranes. Nat Cell Biol 21, 1191-1205
Wolf D, Hofbrucker-MacKenzie SA, Izadi M, Seemann E, Steiniger F, Schwintzer L, Koch D, Kessels MM, Qualmann B
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(2020). The role of membrane-shaping BAR domain proteins in caveolar invagination: from mechanistic insights to pathophysiological consequences. Biochem Soc Trans 48, 137-146
Kessels MM, Qualmann B
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(2021). Functional interdependence of the actin nucleator Cobl and Cobl-like in dendritic arbor development. Elife 10, e67718
Izadi M, Seemann E, Schlobinski D, Schwintzer L, Qualmann B, Kessels MM
