Biophysical Society - July 2014 Newsletter

14

BIOPHYSICAL SOCIETY NEWSLETTER

2014

JULY

Subgroups

selectivity filter of nucleoporins and may play a role in the formation of nucleoporin gels. Mike Rosen , University of Texas Southwestern, Dallas, described liquid demixing of proteins regulating actin polymerization. A protein with repeats of a folded interaction domain and a binding partner with repeats of appropriate binding motifs are able to demix even at low protein concentrations, giv- ing rise to an on-/off-switch. In all of these examples, disordered protein regions mediate assembly and are likely essential for the dynamic, liquid-like character. A biophysical investigation of the molecular basis and meso- scale properties of the aggregated states and the spectrum of functional outcomes promises to substantially improve our understanding of spatial organization and biochemical regulation in cell biology. —Tanja Mittag , Secretary-Treasurer

IDP Liquid Protein Assemblies in Spatial Organization and Ultrasensitive Signaling in Cells Liquid-like cellular “bodies” are light-microscop- ically detectable structures in cells that have a distinct composition from the surrounding cyto- or nucleoplasm but are not enclosed by mem- branes, e.g., P-bodies and nucleoli. The underlying biophysical mechanism for the formation of such bodies may be a liquid demixing phase separa- tion. The interaction of protein molecules with each other can under some conditions be more favorable than with solvent, effectively concentrat- ing the protein in a separate liquid phase, which appears as droplets in a protein-lean solution. It is becoming increasingly clear that some intrinsically disordered proteins are exquisitely tuned to medi- ate liquid demixing, reminiscent of the behavior of synthetic polymers. The symposium with the above title at the 2014 Annual Biophysical Society Meeting in San Francisco, chaired by Tanja Mittag , St. Jude Children’s Research Hospital, Memphis, and Julie Forman-Kay , Hospital for Sick Children, To- ronto, highlighted the role of liquid and gel-like protein states in the cytoplasm, the nucleus, and the extracellular matrix. Forman-Kay discussed microscopy and NMR studies of the liquid demix- ing behavior of a helicase and the relationship of this phenomenon to the formation of germ granules. Regis Pomes’s , Hospital for Sick Children, Toronto, simulations provided insight into the biophysical basis of elastin’s intrinsic ability to self-associate and showed that combined pro- line and glycine content was essential for elastin’s dynamic, disordered assemblies. Edward Lemke , EMBL, Heidelberg, and his group used single molecule fluorescence techniques to demonstrate the highly dynamic nature of the interactions of a FG-nucleoporin with karyopherin. Such weak multivalent interactions may also underlie the

Members in the News

Stefan Hell , Max Planck Institute and Society mem- ber since 1998, has been awarded the Kavli Prize in Nanoscience given by the Norwegian Academy of Science and Letters. Michael Summers , Univer- sity of Maryland, Balti- more County and Society member since 2000, has received the Ruth Kirschstein Diversity in

Science Award from the American Society for Biochemistry and Molecular Biology (ASBMB).