Aerogel and Nanoporoous Materials for Biomolecular Applications ROLAND FALLER Department of Chemical Engineering and Materials Science, UC Davis, Davis, CA 95616, USA. E-mail:
[email protected]
ABSTRACT: Roland Faller visited Tampere University of Technology and the MaxPlanck Institute for Polymer Research in order to plan, coordinate and foster computational collaborations in the framework of the NIRT project “Aerogel and Nanoporoous Materials for Biomolecular Applications”. This travel was necessary to meet and coordinate with the traveling graduate students and the foreign counterparts. The collaboration was very successful as we are preparing joint publications with both partners. Dr. Faller was also invited back to Finland to teach at a summer school which was funded by Finnish counterparts. A new collaboration with the Wihuri Institute in Helsinki is being established including the Faller group and the group of Marja Hyvönen.
INTRODUCTION The travel supplement was awarded for the Project “Aerogel and Nanoporoous Materials for Biomolecular Applications” which is a NIRT award at UC Davis with a sub-award to Stanford University. This project is an integrated multidisciplinary approach to the understanding of the interplay of phospholipid bilayers and aerogels. Over the recent years the experimental member groups were able to reproduce phase coexistence within the bilayer on the aerogel and thus proving the feasibility of the approach. The simulation part of the project lead by the Faller group has successfully been able to describe interaction of bilayers with surfaces to which this international supplement contributed decisively. This will enable us to model the interplay of membranes and aerogels in the next months. The Faller simulation group strives for collaboration with world leaders in molecular modeling with complimentary expertise. Two such groups are the Vattulainen group at Tampere University of Technology and the Deserno group at the MPI for polymer research in Mainz which is a collaborating team on the original NIRT award. Graduate students funded under the NIRT supplement traveled to these groups to get trained in new modeling techniques. Roland Faller traveled there in order to coordinate this research with the corresponding group leaders. We expected that after this travel Chenyue Xing would be proficient in calculating pressure profiles in biomembranes using a technique developed in Tampere and Matthew Hoopes would be proficient in combining computer models of supports with a bilayer
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model developed by Markus Deserno1. Both these primary expectations have been over fulfilled and we are preparing collaborative publications with both groups. The computational partners were selected for their excellence. Ilpo Vattulainen is professor of biophysics at Tampere University of Technology (TUT). His group has a strong expertise in modeling soft matter in general and biomolecular membrane systems in particular. The group is highly involved in studies of cholesterol lipid interactions, interactions of lipids with alcohols and studies of electrophoresis. His group also performs simulation of sphingomyelin (SM) systems, a biologically highly relevant class of lipids, to which Chenyue was now also exposed. The Vattulainen group is clearly one of the leading simulation groups for biomembrane systems. A brief visit to the Deserno group in Germany was added as Matthew Hoopes was visiting the Deserno group for some time. The Max Planck Institute for Polymer Research (MPIP) co-funded this travel. Dr. Markus Deserno at the MPIP has developed a model for water free modeling of free biomembranes. For the research in the NIRT project we are generalizing this model to supported lipid bilayers. In the meeting in Germany we developed a time table for this research. Dr. Roland Faller traveled in a combined trip to both Finland and Germany in the summer of 2007. He spent a week in June in Tampere and Helsinki, Finland and several days in late June in Mainz, Germany. He was invited back to Finland to collaborate and teach at a summer school completely funded by the Finnish collaborators in Espoo, Finland Aug 28-Sep 9, 2007.
RESEARCH ACTIVITIES AND ACCOMPLISHMENTS OF THE INTERNATIONAL COOPERATION The research performed at the partner groups included in Finland modeling of sphingolipids and calculation of pressure profiles which are relevant for the understanding of surface tension effects as well as for anesthesia. Chenyue gained important experience in modeling sphingolipids one of the most important families of lipids. Specific differences in the molecular structure of SM as compared to other main lipid species like phosphatidylcholine where the Faller group already had experience lead to distinctive behavior in membranes which we try to understand. Especially, SM and cholesterol have been observed to be enriched in certain areas of the membrane and to form separate lateral domains, lipid rafts which are an important phenomenon regarding cell signaling and membrane protein transport where the underlying mechanism of the raft formation has been hypothesized to lie in the nature of the interaction between sphingomyelin and cholesterol. The Vattulainen group has also been able to calculate the important quantity of pressure profiles. One of the graduate students in Tampere, Samuli Ollila, developed software for these calculations and trained Chenyue in their application. Together in an integrated fashion Chenyue and Samuli generalized these calculations for new conditions. Roland Faller presented the research of the Davis team in a seminar to the department of physics of Tampere University of Technology in order to allow for a closer collaboration and to disseminate the expertise the Davis team has developed in membrane phase behavior, multiscale modeling and surface interactions. In Germany, Matthew Hoopes was trained in the Espresso simulation package developed by the MPIP as well as in the newest not yet officially released version of the Gromacs software which is the fastest atomistic MD code in the world as one of the major
Gromacs developers, Berk Hess, at the moment is in Mainz. Matthew co-developed with the Deserno group a model for surface interactions of large scale lipid bilayers which is critical for the further studies in the NIRT research. The experience gained in these interactions will thus simplify or even only allow further studies within the NIRT. In both countries Dr. Faller, as well as the graduate students, were fully immersed in the corresponding host institutions. So we all worked one on one integrated in the corresponding research group to maximize the collaborations. Experience was exchanged both ways. We also trained the students and postdocs at the host institutions in the techniques we are leading, which for the purposes here include surface-membrane interactions and multiscale modeling. The research performed abroad will lead to at least two collaborative publications which are in progress at the moment.
Figure 1: Left Comparison of a pressure profile in a supported and an unsupported bilayer, result of the collaboration with TUT, joint data from C. Xing and S. Ollila Right A supported bilayer model developed by Matthew Hoopes.
BROADER IMPACTS OF THE INTERNATIONAL TRAVEL The research performed in Finland on sphingolipids empowers our group to study lipid rafts one of the central problems in molecular biology in much more details as would be possible otherwise. The training of Chenyue on pressure profiles has also a wide range of applicability. The impact of this travel award goes far beyond the direct scientific output. During the stay in Finland Dr. Faller met through Dr. Vattulainen Dr. Marja Hyvönen, a senior scientist, from the Wihuri institute in Helsinki. She instigated a new collaboration between her lab and the Faller lab on LDL cholesterol which would never have happened without this award. Moreover both Dr. Vattulainen and Dr. Deserno will participate in a workshop in Davis next spring in order to continue these collaborations and put the final touches on the publications in progress. We are committed to long-term sustained collaborations with these internationally leading groups. This is true for the partners as well. The group of Dr. Vattulainen invited Dr. Faller to teach at a summer school in Espoo, Finland, in September where Faller was the only speaker invited to give two talks. Matthew Hoopes also participated in this summer school which contributed to sustaining this collaboration. At this school further detail about the instigated research was planned. The travel of Dr. Faller was completely funded by the host institution Dr. Faller is a US permanent resident. He was during the summer travel in Tampere invited by Dr. Vattulainen to be the “opponent”, i.e. major examiner in a PhD defense at Helsinki University of Technology. This experience gave a very direct insight of the
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workings of a Scandinavian university which is strongly different from a US university. An opponent is a member from another, generally foreign, university who has never collaborated with the PhD candidate. S/he is the only person to ask questions in the actual defense exam and eventually decides the grade. The final weekend of the time in Tampere was the midsummer weekend which is the cultural highlight of the year in Finland as well as in the rest of Scandinavia. Faller was introduced to the local culture by the hosts.
DISCUSSION AND SUMMARY In these collaborations we initiated several sub-projects of the current NSF award (grant No. 0506602) during the international travel in Tampere University of Technology, Finland and the MPI for polymer research in Mainz, Germany. Scientifically, we combined our recently proposed supported bilayer model with the sphingomyelin system from TUT. Preliminary data is promising and we expect a joint publication next year. The research using pressure profiles using different scale lipid models is even further along. Chenyue and Samuli have been improving the calculation code developed in Tampere so that it can be used better to fit our work. The research of Matthew Hoopes in Germany is also in the stage of producing data and we start to understand how supports change the behavior of lipid bilayers. This is one of the central theoretical questions from our NIRT grant. The research integration at both sites was clearly critical to empower real collaborations. Only through face to face and social interactions can we build the relationships necessary to perform truly integrated transcontinental research which now can be continued through brief visits and email exchange. In summary, the supplement instigated new lines of research integrated and critical to the main research of the NIRT award.
ACKNOWLEDGEMENTS We gratefully acknowledge funding research and travel through NIRT award CBET 050662 as well as some local co-funding through the Max Planck Institute for polymer research and Tampere University of Technology.
REFERENCES 1.
Ira R. Cooke and Markus Deserno, “Solvent free model for self-assembling fluid bilayer membranes: Stabilization of the fluid phase based on broad attractive tail potentials”, J. Chem. Phys. Vol. 123, No 22, 2005, art no 224710.
2.
C. Xing, S. Ollilla, I. Vattulainen, R. Faller, “Comparing surface tension in models of supported and unsupported bilayers,” in preparation.
3.
M. I. Hoopes, M. L. Longo, M. Deserno, R. Faller, “Interactions of lipid bilayers with a surface using a water-free model,” in preparation
BRIEF BIOGRAPHIES OF RESEARCHERS
Roland Faller received the Diplom in Physics from the University Of Bayreuth, Germany in 1997. He received his Ph.D. in Physics from Johannes Gutenberg University in Mainz Germany in collaboration with the Mac-Planck Institute for Polymer Research in 2000, respectively. He then was a post-doctoral fellow at The University of Wisconsin in the department of Chemical Engineering. In 2002 he has been appointed Assistant Professor of Chemical Engineering and Materials Science at the University of California Davis. He was promoted to Associate Professor with tenure in 2006.
