Markus Deserno Associate Professor Ph.D., Max-Planck-Institute for Polymer Research Email: deserno@andrew.cmu.edu Phone: 412 268 4401 Fax: 412 681 0648

    Biological systems belong to the most fascinating and mysterious entities to be found in our universe, and yet their functioning ultimately rests entirely on very well known laws of nature. In order to understand how biological systems work we do not need to discover previously unknown bits of physics and chemistry; the task is rather to piece the puzzle together and learn how simple laws can explain complex phenomena. Biological Physics is thus a synthetic science, much like Statistical Physics, from whose arsenal of methods it frequently and heavily borrows.

    In my research I study one particular biological system: the lipid bilayer. This is the basic structure underlying the outer membrane of every living cell, as well as many other membraneous structures inside eucaryotic cells (such as the nucleus, the endoplasmic reticulum, or the Golgi apparatus). Its architecture is deceptively simple: it consists of a five nanometer thin bilayer of lipid molecules, which assemble in such a fashion that the hydrophilic ("water-loving") head groups shield the hydrophobic ("water-fearing") hydrocarbon tails from the surrounding water. Its low-dielectric interior makes it an excellent insulator for ions. The fact that lipids self-assemble instead of being chemically linked together leaves the bilayer (at not too low temperatures) in a fluid state, permitting it to assume many different shapes, frequently switch between them, and routinely change its topology. Its hydrocarbon core, similar in density and composition to a polymer melt, equips it with a soft elastic modulus that implies a bending resistance equal to a few tens times the thermal energy -- a perfect value to be both thermodynamically stable and mechanically deformable. This is an ideal material for nanotechnology, and nature found out about it first, four billion years ago.

    In my research I use both theoretical and computational techniques to study lipid membranes. On the theoretical side I use a continuum elastic description, valid on length scales beyond a few times the membrane thickness. We heavily rely on differential geometry, since this is the perfectly appropriate language to deal with curved surfaces. What might look unusual turns out to be a great blessing, because valuable connections between geometry and physics are readily visible, rather than being hopelessly hidden by some arbitrary choice of surface coordinates.

    On the computational side I mostly use coarse-grained simulations. This means that the physical system is not represented on the computer in atomic detail. Rather, a much smaller number of degrees of freedom is used to describe a lipid or a protein. This renouncement of chemical resolution implies that questions dependent on it cannot be addressed. However, on sufficiently large length scales such detail hardly matters, and the physical properties relevant at this scale, for instance the bending rigidity, can be accounted for very appropriately. The benefit to be reaped from this simplified description is the ability to study much larger systems on much longer time scales and to access a new arena for physical questions. Many of them invariably turn out to have a biological significance.

Benedict J. Reynwar, Gregoria Illya, Vagelis A. Harmandaris, Martin M. Müller, Kurt Kremer, and Markus Deserno: Aggregation and vesiculation of membrane proteins by curvature-mediated interactions, Nature 447, 461–464 (2007).

Martin M. Müller, Markus Deserno, and Jemal Guven: Contact lines for fluid surface adhesion, Phys. Rev. E 76, 011605 (2007).

Vagelis A. Harmandaris and Markus Deserno: A novel method for measuring the bending rigidity of model lipid membranes by simulating tethers, J. Chem. Phys. 125, 204905 (2006).

Davood Norouzi, Martin M. Müller, and Markus Deserno: How to determine local elastic properties of lipid bilayer membranes from atomic-force-microscope measurements: A theoretical analysis, Phys. Rev. E 74, 061914 (2006).

Siegfried Steltenkamp, Martin M. Müller, Markus Deserno, Christian Hennesthal, Claudia Steinem, and Andreas Janshoff: Mechanical properties of pore-spanning lipid bilayers probed by atomic force microscopy, Biophys. J. 91, 217–226 (2006).

Ira R. Cooke and Markus Deserno: Coupling between lipid shape and membrane curvature, Biophys. J. 91, 487–495 (2006).

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. 123, 224710 (2005).

Ira R. Cooke, Kurt Kremer, and Markus Deserno: Tunable generic model for fluid bilayer membranes, Phys. Rev. E 72, 011506 (2005).

Martin M. Müller, Markus Deserno, and Jemal Guven: Interface mediated interactions between particles – a geometrical approach, Phys. Rev. E 72, 061407 (2005).

Martin M. Müller, Markus Deserno, and Jemal Guven: Geometry of surface mediated interactions, Europhys. Lett. 69, 482–488 (2005).

Igor M. Kulic, Denis Andrienko, and Markus Deserno: Twist-bend instability for toroidal DNA condensates, Europhys. Lett. 67, 418–424 (2004).

Shelly Tzlil, Markus Deserno, William M. Gelbart, and Avinoam Ben-Shaul: A Statistical-Thermodynamic Model of Viral Budding, Biophys. J. 86, 2037–2048 (2004).

Markus Deserno: Elastic deformation of a fluid membrane upon colloid binding, Phys. Rev. E 69, 031903 (2004).

Amado Cordova, Markus Deserno, William M. Gelbart, and Avinoam Ben-Shaul: Osmotic Shock and the Strength of Viral Capsids, Biophys. J. 85, 70–74 (2003).

Markus Deserno and Thomas Bickel: Wrapping of a spherical colloid by a fluid membrane, Europhys. Lett. 62, 767–773 (2003).