Regulation des okulären Surfactant-Systems und dessen Bedeutung für das Auge
Final Report Abstract
In the course of this project, protein structure models for the two putative surfactant proteins SP-G and SP-H could be obtained by computational modeling approaches. These protein models could be complemented with posttranslational modifications on the basis of sequence based prediction tools. This step was necessary for further investigations, because the modifications are described to be very important for the function of already known surfactant proteins. The stability of the protein models without and with modifications was validated by molecular dynamic (MD) simulations. With the help of the final protein structure models, specific antibodies could be produced, which led to the first successful localization of SP-G and SP-H on the protein level in different human tissues by immunohistochemical staining. According to these studies, SP-G and SP-H are part of the tear film and lung surfactant system, so that for MD simulations of both proteins in their natural environment to study their characteristics and function, one of these systems had to be reproduced by a simulation setup with appropriate settings. After the construction of a tear film system failed due its very complex composition and layout, the lung surfactant system was modeled. For this, a stable monolayer system consisting of the major lung surfactant lipid DPPC was established, which was demonstrated to be suitable for protein-lipid simulations. The unmodified and modified protein models were then placed near this lipid layer and simulated for 50 ns, starting from different initial orientations. These simulations revealed that SP-G and SP-H are stable in this environment, regardless of the posttranslational modifications. Furthermore, the simulations clearly showed that both proteins could in fact interact with lipids, which is a prerequisite for a surfactant protein. More in detail, it could be observed that the predicted posttranslational modifications can influence the region as well as the strength of the protein-lipid interaction. Altogether, the localization of SP-G and SP-H, their ability to interact with a lipid system and their posttranslational modification influenced surface characteristics and activity supports the hypothesis that SP-G and SP-H are indeed surfactant proteins, whose detailed investigation can give new insights into the molecular mechanism of surfactant systems. The here presented results are not of any industrial or economical use at this point, but they represent a valuable basis for further research on the topic of surfactant proteins. Simulations with more complex surfactant model systems (lipid mixtures, tear film layout), investigation of protein-protein interactions between SP-G, SP-H and other surfactant proteins as well as detailed functional studies, in each case in conjunction with experimental work, could promote the research on this topic in future and lead to new knowledge regarding to diseases in surfactant systems and their possible therapy.
Publications
- Molekülsimulationen von Surfactant-Proteinen. Ophthalmologische Nachrichten, 12. 2012 [Dr. Gerhard Mann SICCA Förderpreis]
Felix Rausch
- „SP-G“, a putative new surfactant protein – tissue localization and 3D structure, PlosOne, 2012, 7, e7789
Felix Rausch, Martin Schicht, Friedrich Paulsen, Ivan Ngueya, Lars Bräuer and Wolfgang Brandt
(See online at https://doi.org/10.1371/journal.pone.0047789)
