Publikationsserver der Universitätsbibliothek Marburg

Titel:On the Morphology and Dynamics of Purple Membranes at the Solid-Liquid Junction
Autor:Baumann, Roelf-Peter
Weitere Beteiligte: Hampp, Norbert (Prof. Dr.)
Veröffentlicht:2011
URI:https://archiv.ub.uni-marburg.de/diss/z2011/0608
DOI: https://doi.org/10.17192/z2011.0608
URN: urn:nbn:de:hebis:04-z2011-06084
DDC:540 Chemie
Titel (trans.):Über die Morphologie und Dynamik von Purpurmembranen an der Fest-Flüssig-Grenzfläche
Publikationsdatum:2011-10-21
Lizenz:https://rightsstatements.org/vocab/InC-NC/1.0/

Dokument

Schlagwörter:
Bakteriorhodopsin, bacteriorhodopsin, purple membrane, Purpurmembran

Summary:
In dependence on the substrate bacteriorhodopsin within purple membrane at the solid-liquid junction is prone to dynamical transitions which were observed for the first time and found to be responsible for, in part, large scale morphological changes of the adsorbed purple membrane patches. Extrinsic and intrinsic factors could be identified to govern the interplay of morphology and dynamics, which lead to the deduction of a general, substrate independent stability criterion applicable to purple membranes comprising BR-wild-type and variants alike. Surface free energy and substrate roughness are key extrinsic parameters in this context that enable or slow down dynamical transitions within solid-supported PMs. Conversion of BR into a chloride pump by a single-point mutation seriously affects its crystallization tendency and reveals how intrinsic factors figure into the observed interplay. Interestingly, upon stabilization of the tertiary structure of BR-D85T, intrinsically mediated by chloride binding in the retinal binding pocket, the ability of PM-D85T to form coherent crystalline domains can be restored. PM-D85T also allowed for purple membrane bending of various photocycle intermediates to be studied in thermal equilibrium at the solid-liquid junction. Side discrimination via SMFS and EFM showed that PM-D85T is bent cytoplasmic side out in the M2 photointermediate and passes through a flat topology in the N intermediate in order to bend extracellular side out in the final O photointermediate. The different bending modes observed illustrate a reoccurring motif in nature of how the form of BR follows its function which is that of a vectorial proton pump transfering protons from the cytoplasmic to the extracellular medium. Membrane curvature was further analyzed to reveal that smaller membranes are strongly influenced by extrinsic constraints imposed by the substrate surface. Larger membranes on the contrary retain a characteristic curvature which is dependent on the physicochemical conditions and the corresponding shape of BR, thereby demonstrating that solely the intrinsic shape changes of the embedded proteins are responsible for the macroscopically bent nature of the membranes. From a nanobiotechnology perspective, PM represents a supramolecular actuator set in motion by intrinsic and extrinsic influences, which opens a wide field of possible applications. One example would be as chemomechanical transducer, which upon a pH-shift changes shape and thereby interacts with its environment. These interaction capabilities place purple membrane in the context of other molecular machines and supramolecular switches. The observed and tentatively tunable dynamical transitions and the ability to reversibly control PM crystallinity might allow for the preparation of larger artificial membranes, which might be used for data storage or photovoltaic applications or serve as template in the construction of novel nanobiomaterials such as photonic crystals.


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