Adaptive compartments with life-like behaviour
Professor Jan Van Hest, Technische Universiteit Eindhoven, The Netherlands
Compartmentalization is generally regarded as one of the key prerequisites for life. In living cells, not only the cell itself is a compartment, with its properties controlled by the semipermeable cell membrane, but also the organelles play a crucial role in protecting and controlling biological processes. To better understand the role of compartmentalization, there is clear need for model systems that can be adapted in a highly controlled fashion, and in which life-like properties can be installed. Polymer-based compartments are robust and chemically versatile, and as such are a useful platform for the development of life-like compartments. In this contribution both an artificial organelle and cell system will be discussed. The artificial organelles are composed of biodegradable amphiphilic block copolymers that self-assemble into vesicular structures. These so-called polymersomes are loaded with enzymes and are semi-permeable for small molecule substrates. Upon introduction in living cells, they affect metabolic pathways as artificial organelles. A different type of polymersome is created via a shape change process in which a bowl-shaped structure is obtained. Within the cavity of the bowl enzymes are loaded which provide the nanostructure with motility upon conversion of chemical energy into kinetic energy. The synthetic cell platform is composed of a complex polymer coacervate, stabilized by a biodegradable block copolymer. The specific feature of the polymer membrane is its semipermeable character. Enzymes inside the protocell can therefore still be reached by their substrates, and small molecule products can be excreted. This allows protocell communication with this robust synthetic platform.
Biomimetic synthesis of artificial magnetosomes
Dr Sarah Staniland, University of Sheffield, UK
Model systems for membraneless subcellular organelles: Compartmentalization of biomolecules and reactions by liquid-liquid phase coexistence
Professor Christine Keating, Penn State University, USA
Protein design in the cell: towards a synthetic proteome
Professor Dek Woolfson, University of Bristol, UK
Protein design, that is, the construction of entirely new protein sequences that fold into prescribed structures, has come of age. It is now possible to design proteins de novo using simple rules of thumb or computational design methods. The designs can be made rapidly via peptide synthesis or the expression of synthetic genes; and the resulting proteins can usually be characterised all the way through to high-resolution X-ray crystal structures. Contemporary questions in the protein-design field include: What do we do with these new-found skills? What protein structures and functions do we target? How far can we move past the confines of natural protein structures and functions? And, how can we take protein design from an exercise largely done in silico and in vitro into a truly synthetic biology and take it in vivo? This talk will address these questions with reference to simple through to complex and functional protein designs that we have explored over the past 5–10 years. These use a straightforward protein structure, called the alpha-helical coiled coil, which are bundles of 2 or more alpha helices found in many protein-protein interactions. As such it provides an excellent basis for building proteins from the bottom up. The vast majority of coiled-coil designs have been based on simple rules of thumb learnt from natural proteins or derived empirically through experiment. These rules relate sequence to structure to guide the specification of coiled-coil oligomerization state, strand orientation, partner selection, and, to some extent, stability. This has been extremely informative and productive, and design and engineering is probably more advanced for coiled coils than for any other protein structure. However, to move past the low-hanging fruit of coiled-coil design, and into the so-called dark matter of protein structures, we will all have to learn new tricks. To address this Professor Woolfson has begun to tackle coiled-coil design parametrically using computational methods. Professor Woolfson has developed easy-to-use computational modelling tools and a more-sophisticated suite of programs called ISAMBARD that allow the rapid generation and optimisation of protein designs in silico. The first part of the talk will describe how a serendipitous discovery of a 6-stranded alpha-helical barrel led his group to develop these computational methods, and how they have used these to deliver entirely new non-natural protein structures predictably. It will show the utility of this approach to make water-soluble protein-like barrels, which the group has engineered to form materials, bind small molecules, and catalyse simple reactions. Secondly, Professor Woolfson will demonstrate how we might take protein design in vivo with recent work with the Warren lab (Kent) and the Verkade lab (Bristol). He has engineered hybrids of a de novo heterodimer and a natural component of bacterial microcompartments. When expressed in E. coli, the hybrid assemblies to form a cytoscaffold that permeates the cells, and can act as a support for the co-localisation of functional enzymes.