Biophysical Society Thematic Meeting - October 25-30, 2015

Polymers and Self Assembly: From Biology to Nanomaterials

Monday Speaker Abstracts

How to Build a Septin Filament Richard Garratt . University of Sao Paulo, Brazil

Monomeric septins polymerize into membrane associating hetero-filaments which are involved in membrane remodelling events and barrier formation. The human genome includes 13 genes coding for septins that can be divided into four different groups leading to hundreds of different possible combinations for hetero-filament formation. The filaments themselves are stabilized via two different types of inter-subunit interface (G and NC) which alternate along the main axis. In an attempt to understand the rules which underpin spontaneous filament assembly we have used crystallographic approaches allied to a series of complementary biophysical techniques. In essence, the problem of self assembly can be reduced to understanding the structural basis for specificity at each of the five different interfaces which appear between individual septins along a filament composed of four different monomers. We demonstrate that a C-terminal coiled-coil domain is important for the recognition of partner septins at one of the NC interfaces as well as contributing to the formation of higher-order assemblies. Studies of septins bound to both GTP and GDP show that the two types of interface are interconnected as a result of an unexpected shift in the register of a central β-sheet strand on GTP hydrolysis. This is predicted to affect membrane binding. In summary, our data suggest mechanisms for self-assembly, filament bundling and the importance of GTP binding and hydrolysis for membrane association. phosphorylated by S-phase cyclin-Cdk1-Cks1. The processivity is modulated by phosphorylation/dephosphorylation of a priming site and a diversional site by two kinases and a phosphatase of stress pathways. Both the priming site and the diversional site compete for binding to Cks1. This mechanism demonstrates how external signals can be integrated into the Cdk1 control system via multi-branched signal-processing modules based on multisite phosphorylation networks. Such transistor-like modules are possibly ubiquitous and could regulate many cellular events.

The Varied Geometries of ParM Cytomotive Filaments in Bacterial Plasmid Segregation Robert Robinson Institute for Molecular & Cell Biology, Singapore No abstract

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