Self-Assembly at a Membrane

Self-assembly is a process by which the interactions between a disordered collection of sub-units drives them to spontaneously form an ordered structure. Many of the components of cells, the building blocks of all organisms, are self-assembled, often from proteins, meaning that such processes are fundamental to life. Correspondingly, there are a wide variety of human diseases that are related to the malfunctioning of self-assembly, not to mention the countless maladies arising from viruses, self-assembled pathogens. Understanding self-assembly may help to develop cures for these myriad afflictions. An important part of creating this understanding is to investigate the underlying physics. In this project we aim to contribute towards this goal. Physics-based studies have focussed on self-assembly in the bulk. However, the assembly of proteins generally occurs within cells, which are surrounded by a membrane, a fluctuating surface, and also contain many other membrane-bound components. There is evidence that the self- assembly of a broad range of structures, including viral cores, clathrin and actin, is strongly influenced by membranes. Earlier physics investigations have largely ignored this important aspect; with there being only very limited work on a few specific examples, where insertion into the membrane occurs. We will direct our attention to protein structures, whose assembly-processes are affected by membranes, but which are not, or are only to a small extent, inserted into them. Given the lack of previous work, it is crucial to form a picture of the physical mechanisms that are common to such systems. To this end, we choose to employ coarse- grained simulation models that will allow the explorations of a wide range of parameters so that the basic physics may be identified. For the self-assembling proteins, we will use patchy-particles, which have been successfully used to model the assembly of viral cores and clathrin. Membranes will be included using network models, which may be easily coupled to patchy-particles and provide sufficient detail for our purposes, whilst remaining relatively computationally efficient. We intend to perform simulations using Monte Carlo and Brownian dynamics to investigate equilibrium structures and Multiparticle-collision dynamics, a method that allows the efficient inclusion of hydrodynamic interactions, to study dynamics.