TY - JOUR A1 - Fussmann, Gregor F. A1 - Blasius, Bernd T1 - Community response to enrichment is highly sensitive to model structure N2 - Biologists use mathematical functions to model, understand, and predict nature. For most biological processes, however, the exact analytical form is not known. This is also true for one of the most basic life processes, the uptake of food or resources. We show that the use of a number of nearly indistinguishable functions, which can serve as phenomenological descriptors of resource uptake, may lead to alarmingly different dynamical behaviour in a simple community model. More specifically, we demonstrate that the degree of resource enrichment needed to destabilize the community dynamics depends critically on the mathematical nature of the uptake function. Y1 - 2005 UR - http://www.agnld.uni-potsdam.de/~bernd/papers/BiolLett1.pdf ER - TY - JOUR A1 - Betke, Alexander A1 - Lokstein, Heiko T1 - Two-photon excitation spectroscopy of photosynthetic light-harvesting complexes and pigments JF - Faraday discussions N2 - In addition to (bacterio)chlorophylls, (B)Chls, light-harvesting complexes (LHCs) bind carotenoids, and/or their oxygen derivatives, xanthophylls. Xanthophylls/carotenoids have pivotal functions in LHCs: in stabilization of the structure, as accessory light-harvesting pigments and, probably most importantly, in photoprotection. Xanthophylls are assumed to be involved in the not yet fully understood mechanism of energy-dependent (qE) non-photochemical quenching of Chl fluorescence (NPQ) in higher plants and algae. The so called "xanthophyll cycle" appears to be crucial in this regard. The molecular mechanism(s) of xanthophyll involvement in qE/NPQ have not been established, yet. Moreover, excitation energy transfer (EET) processes involving carotenoids are also difficult to study, due to the fact that transitions between the ground state (S-0, 1(1)A(g)(-)) and the lowest excited singlet state (S-1, 2(1)A(g)(-)) of carotenoids are optically one-photon forbidden ("dark"). Two-photon excitation spectroscopic techniques have been used for more than two decades to study one-photon forbidden states of carotenoids. In the current study, two-photon excitation profiles of LHCII samples containing different xanthophyll complements were measured in the presumed 1(1)A(g)(-) -> 2(1)A(g)(-) (S-0 -> S-1) transition spectral region of the xanthophylls, as well as for isolated chlorophylls a and b in solution. The results indicate that direct two-photon excitation of Chls in this spectral region is dominant over that by xanthophylls. Implications of the results for proposed mechanism(s) of qE/NPQ will be discussed. Y1 - 2019 U6 - https://doi.org/10.1039/c8fd00198g SN - 1359-6640 SN - 1364-5498 VL - 216 SP - 494 EP - 506 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Bapolisi, Alain Murhimalika A1 - Kielb, Patrycja A1 - Bekir, Marek A1 - Lehnen, Anne-Catherine A1 - Radon, Christin A1 - Laroque, Sophie A1 - Wendler, Petra A1 - Müller-Werkmeister, Henrike A1 - Hartlieb, Matthias T1 - Antimicrobial polymers of linear and bottlebrush architecture BT - Probing the membrane interaction and physicochemical properties JF - Macromolecular rapid communications : publishing the newsletters of the European Polymer Federation N2 - Polymeric antimicrobial peptide mimics are a promising alternative for the future management of the daunting problems associated with antimicrobial resistance. However, the development of successful antimicrobial polymers (APs) requires careful control of factors such as amphiphilic balance, molecular weight, dispersity, sequence, and architecture. While most of the earlier developed APs focus on random linear copolymers, the development of APs with advanced architectures proves to be more potent. It is recently developed multivalent bottlebrush APs with improved antibacterial and hemocompatibility profiles, outperforming their linear counterparts. Understanding the rationale behind the outstanding biological activity of these newly developed antimicrobials is vital to further improving their performance. This work investigates the physicochemical properties governing the differences in activity between linear and bottlebrush architectures using various spectroscopic and microscopic techniques. Linear copolymers are more solvated, thermo-responsive, and possess facial amphiphilicity resulting in random aggregations when interacting with liposomes mimicking Escheria coli membranes. The bottlebrush copolymers adopt a more stable secondary conformation in aqueous solution in comparison to linear copolymers, conferring rapid and more specific binding mechanism to membranes. The advantageous physicochemical properties of the bottlebrush topology seem to be a determinant factor in the activity of these promising APs. KW - antimicrobial polymers KW - bottlebrush copolymers KW - liposomes KW - membrane KW - interactions KW - quartz crystal microbalance Y1 - 2022 U6 - https://doi.org/10.1002/marc.202200288 SN - 1521-3927 SN - 1022-1336 VL - 43 IS - 19 PB - Wiley-VCH CY - Weinheim ER - TY - THES A1 - Stange, Maike T1 - A study on Coronin-A and Aip1 function in motility of Dictyostelium discoideum and on Aip1 interchangeability between Dictyostelium discoideum and Arabidopsis thaliana T1 - Studie über die Funktion von Coronin-A und Aip1 bei der Motilität von Dictyostelium discoideum und zur Aip1-Austauschbarkeit zwischen Dictyostelium discoideum und Arabidopsis thaliana N2 - Actin is one of the most highly conserved proteins in eukaryotes and distinct actin-related proteins with filament-forming properties are even found in prokaryotes. Due to these commonalities, actin-modulating proteins of many species share similar structural properties and proposed functions. The polymerization and depolymerization of actin are critical processes for a cell as they can contribute to shape changes to adapt to its environment and to move and distribute nutrients and cellular components within the cell. However, to what extent functions of actin-binding proteins are conserved between distantly related species, has only been addressed in a few cases. In this work, functions of Coronin-A (CorA) and Actin-interacting protein 1 (Aip1), two proteins involved in actin dynamics, were characterized. In addition, the interchangeability and function of Aip1 were investigated in two phylogenetically distant model organisms. The flowering plant Arabidopsis thaliana (encoding two homologs, AIP1-1 and AIP1-2) and in the amoeba Dictyostelium discoideum (encoding one homolog, DdAip1) were chosen because the functions of their actin cytoskeletons may differ in many aspects. Functional analyses between species were conducted for AIP1 homologs as flowering plants do not harbor a CorA gene. In the first part of the study, the effect of four different mutation methods on the function of Coronin-A protein and the resulting phenotype in D. discoideum was revealed in two genetic knockouts, one RNAi knockdown and a sudden loss-of-function mutant created by chemical-induced dislocation (CID). The advantages and disadvantages of the different mutation methods on the motility, appearance and development of the amoebae were investigated, and the results showed that not all observed properties were affected with the same intensity. Remarkably, a new combination of Selection-Linked Integration and CID could be established. In the second and third parts of the thesis, the exchange of Aip1 between plant and amoeba was carried out. For A. thaliana, the two homologs (AIP1-1 and AIP1-2) were analyzed for functionality as well as in D. discoideum. In the Aip1-deficient amoeba, rescue with AIP1-1 was more effective than with AIP1-2. The main results in the plant showed that in the aip1-2 mutant background, reintroduced AIP1-2 displayed the most efficient rescue and A. thaliana AIP1-1 rescued better than DdAip1. The choice of the tagging site was important for the function of Aip1 as steric hindrance is a problem. The DdAip1 was less effective when tagged at the C-terminus, while the plant AIP1s showed mixed results depending on the tag position. In conclusion, the foreign proteins partially rescued phenotypes of mutant plants and mutant amoebae, despite the organisms only being very distantly related in evolutionary terms. N2 - Actin ist eines der am stärksten konservierten Proteine in Eukaryoten und sogar Prokaryoten weisen Aktin-ähnliche Proteine mit filamentbildenden Eigenschaften auf. Aufgrund dieser Gemeinsamkeiten teilen Aktin-modulierte Proteine vieler Arten ähnliche strukturelle Eigenschaften und vermutlich auch Funktionen. Die Polymerisierung und Depolymerisation von Aktin sind kritische Prozesse für eine Zelle, da sie zu Zellformänderungen beitragen können, um sich an die Umgebung anzupassen und Nährstoffe sowie zelluläre Komponenten innerhalb der Zelle zu bewegen und zu verteilen. Inwieweit die Funktionen von Aktin-bindenden Proteinen zwischen entfernt verwandten Arten funktionell konserviert sind, wurde jedoch nur in wenigen Fällen untersucht. In dieser Arbeit wurden Funktionen von Coronin-A (CorA) und Actin-interagierendem Protein 1 (AIP1), zweier an der Aktindynamik beteiligter Proteine, charakterisiert. Darüber hinaus wurde die Austauschbarkeit und Funktion von AIP1 in zwei phylogenetisch entfernten Modellorganismen untersucht. Die Blütenpflanze Arabidopsis thaliana (kodiert für zwei Homologe: AIP1-1 und AIP1-2) und die Amöbe Dictyostelium discoideum (kodiert für ein Homolog: DdAip1) wurden ausgewählt, weil die Funktionen ihrer Aktin-Zytoskelette in mehreren Aspekten verschieden sein könnten. Funktionelle Analysen zwischen Arten wurden für AIP1-Homologe durchgeführt, da Blütenpflanzen kein CorA Gen tragen. Im ersten Teil der Arbeit wurde die Wirkung von vier verschiedenen Mutationsmethoden auf die Funktion des CorA-Proteins und des resultierenden Phänotyps in D. discoideum in zwei genetischen Knockouts, einem RNAi Knockdown und einem durch chemisch induzierte Delokalisierung (CID) erzeugten Mutanten geprüft. Die Vor- und Nachteile der Methoden zur Motilität, des Aussehens und der Entwicklung der Amöben wurden untersucht. Die Ergebnisse zeigten, dass nicht alle beobachteten Eigenschaften mit der gleichen Intensität beeinflusst wurden. Hierbei wurde eine neue Methodenkombination aus selektionsgebundener Integration und CID etabliert. Im zweiten und im dritten Teil der Arbeit wurde der Austausch von AIP1 zwischen Pflanze und Amöben durchgeführt. Die zwei A. thaliana-Homologe AIP1-1 und AIP1-2 wurden auf Funktionalität in D. discoideum geprüft. In Aip1-defizienten Amöben war die Rettung mit AIP1-1 effektiver als bei AIP1-2. Die Hauptergebnisse der Arbeit wiesen darauf hin, dass AIP1-2 im aip1.2-1 act7 Mutantenhintergrund die effizienteste Rettung zeigte, während A. thaliana AIP1-1 effizienter rettete als DdAip1. Die Auswahl der Tagging-Site war für die AIP1-Funktion bedeutend, da sterische Hinderung eine Rolle spielen könnte. DdAip1 war weniger effektiv, wenn es am C-Terminus fusioniert war, während die Proteinfusionen der A. thaliana AIP1s je nach Position der „tags“ unterschiedliche Ergebnisse zeigten. Zusammenfassend retteten die fremden Proteine teilweise Phänotypen von mutierten Pflanzen und mutierten Amöben, obwohl die Organismen evolutionär weit entfernt verwandt sind. KW - actin KW - cell motility KW - plant growth KW - selection-linked integration KW - chemically induced dislocation KW - interspecies interchange KW - Aktin KW - Zellmotilität KW - Pflanzenwachstum KW - Selection-Linked Integration KW - chemisch-induzierte Dislokation KW - Austausch zwischen zwei Spezies Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-628569 ER -