Membrane Pharmacy Structure Dynamics  Research group : Priv.Doz. Dr. Thomas Nawroth  BioEnergetics

Fig.1: The bioenergetic network of membrane proteins delivers 99% of the energy (ATP and reduction work, NADH) for cellular functions in those organisms capable of respiration or photosynthesis. This is one of the four common cellular reaction cycles, which are linked by common substrates and products (Acteyl-CoEnzyme-A, NADH, ATP) (after T20).

The objects of science by the MPSD group are proteins capable of molecular motion and membranes. Those systems are the constituents of the bioerergetic system of all cells beein capable of photosynthesis or respiration, e.g. man. As depicted in Fig.1, this system delivers about 99% of the energy in those biological systems. A further example of motile systems are the membrane receptors, which carry information from outside the cell to the interior by a series of molecular motions, i.e. conformational changes. Figure2 concludes some common features of bioenergetic systems: they contain an ion-tight membrane, ion pumping proteins and energy converters. Thus the bioenergetic proteins bear at least two different, but energetically coupled activities. These membrane proteins couple the (photo)chemical reaction and the ion translocation by molecular motion. Between the two processes the energy, e.g. 30 kJ/mole, is stored inside the protein. In this respect the bioenergetic ion pumps resemble the motor proteins, e.g. in muscle. In the case of ATP-synthase the catalytic domains bear significant homology to several motor proteins, e.g. Kinesin, Dynein, the ribosomal elongation factor EF-Tu and the intracellular switch ras-p21. Additionally the bioenergetic proteins show significant molecular regulation, i.e. a gear of the catalytic activity. In both cases, energy transfer reaction and regulation, the structure-function relation is the key for the biological activity. Thus the investigation of molecular structure with the isolated purified proteins is a focus of science. This is done by neutron- and X-ray scattering of solutions or diffraction. In case of heterogenous membranes freeze fracture electron microscopy is required. In case of ATP-synthase and its catalytic head, F₁ATPase, from the aerobic bacterium Micrococcus luteus a scheme of conformational changes during regulation was found and a film of molecur motion during enzymatic ATP-hydrolysis was estimated.
 

Fig.1: The bioenergetic system consists of membranes, which are impermeable to special ions (H+, Na+) and a network of incorporated energy converting membrane proteins, which are ion pumps. In most organisms these are proton pumps,  whereas sodium pumps are present in some special systems (e.g. extremophiles) and probably in anicient species. The energy converting membrane proteins have some common features: i) they bear at least two different active domains, one translocation the ions across the membrane, the other catalyzing a (photo)chemical reaction or mechanical work; ii) the energy converters are capable of molecular motion, which connects the two reactions (transport and catalysis); iii) the energy is stored inside the protein between the ion transport andd catalysis processes, probable in an energized protein conformation, i.e. a metastable state. The energized state of the whole system is stored in the "energized state of the membrane", i.e. an electrochemical proton potential difference sufficient for ATP synthesis :  delta-p > 100 mV. Thus the primary cellular energy storage is done by a physical membrane state and not in a chemical compound. The proton pump ATP-synthase converts this local energy into a membrane-independent compound: AdenosineTriPhosphate, ATP. By this reaction the energy od respiration or photosynthesis becomes available to the enzymes inside the cell, e.g. in the cytoplasm. Many species have a H+/Na+exchanger which links the proton- to the sodium-world (after T20).