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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