Gelsolin and actin from crystal structure shown as black and blue ribbon with modeled SANS data for gelsolin and the actin dimer of the GA2 complex shown as dark grey and light grey balls, respectively.
Master’s student, Ryan Oliver, finished writing and successfully defended his thesis work, (see abstract below). He was accepted into the Ph. D. program in Chemistry at the U. Virgina beginning in the Fall 2010. He will move to Charlottesville, VA in June and begin working with Dr. Linda Columbus, who has offered him a summer position in his lab.
Contrast is a demonstration on the concept of light scattering and contrast matching that Ryan used in his defense.
Constraints for Building Structural Models of Gelsolin, an Actin Dimer, and their Complex in Solution using Small-angle Scattering Data
Abstract:
Actin, a 42kDa globular protein commonly recognized for its role in muscle cell contraction, is an essential component of the cellular cytoskeleton in nearly all eukaryotic cells. In non-muscle cells, actin forms dynamic networks responsible for vital cellular functions such as intracellular localization and transport, as well as cellular motility events. Actin’s role in these processes is achieved through its ability to rapidly polymerize to filamentous (F-)actin and de-polymerize back to monomeric globular (G-)actin in a tightly-regulated fashion. Gelsolin is one of several actin-binding proteins whose function is to regulate the dynamic assembly and disassembly of F-actin via nucleation, severing and capping mechanisms. Gelsolin is bilobal and compact, composed of six homologous domains, but unhinges to accept actin monomers and nucleate filament formation following activation by Ca+2. We have small angle X-ray scattering (SAXS) data on Ca+2-activated gelsolin and the Ca+2-activated gelsolin in complex with 2 molar equivalents of G-actin. Small-angle neutron scattering (SANS) contrast variation data was collected on a similar complex utilizing recombinantly expressed human plasma gelsolin from cells grown in 60% deuterated media. These data provide structural constraints for modeling the actin-bound full-length Ca+2-gelsolin as well as the gelsolin-bound actin dimer independently. These SAS-constrained models provide new insights into the regulatory activity of gelsolin and a greater understanding of the mechanism by which gelsolin nucleates F-actin formation with broad implications as to the mechanism for actin polymerization in general.