Jorge Viamontes

Contact:
Viamontes@gmail.com

Education:
AA Miami Dade Community College
B.A University of Rochester (Physics and Mathematics)
M.A Indiana University (Physics)
Ph.D. Brown University 2005

Research Project:
The protein actin was discovered on 1943 by F.B Straub as one of the major components of the muscle tissue. Actin is later found extensively in the cytoplasm of virtually all eukaryotic cells. Actin plays an important role in maintenance of cell shape, cell motility, and cytokinesis. Central to many functions of actin is its polymerization property. The 42 kd monomers can rapidly self-assemble to form long filaments, called F-actin. Actin filaments in the cytoplasm are found in various forms: isotropic gel like, liquid crystalline domains, crystalline loose bundles, etc. Understanding this whole range of network structures, as well as many dynamic aspects of actin assembly forms the physical basis of research on cell motility. In vitro, F-actin forms a nematic liquid crystalline phase at slightly above 2 mg/ml. The formation of liquid crystalline phases for a suspension of rodlike molecules was predicted theoretically by Onsanger 1949. Several recent studies have confirmed many aspects of the theoretical predictions for F-actin solutions. For instance, the onset actin concentration for the isotropic to nematic transition has been found to be inversely proportional to the average filament length. These have also been bulk measurements suggesting a concentration range in which F-actin consists of partially aligned domains.
The goal of our project is to measure local alignment of actin filaments, the co-existing domains of aligned filaments (nematic) and filaments with random orientations (isotropic), all of which in close correlation with variation of local protein concentrations. Through these measurements, we discover surprising features, suggesting that the I-N transition of F-actin may be of 2nd or even higher order. A non-first order transition can be explained through the resent theoretical work of John Toner, Lammert, and Rokhsar. In addition, we demonstrate interesting dynamics of actin filaments in the nematic state, by mixing a small number of short actin filaments into unlabelled F-actin of the same average filament length. Our project includes the diffusion coefficient determination for filaments polymerized under ATP and ADP buffer conditions. Striking results were obtained; Suggesting that filaments under ATP buffer conditions diffuse faster than under ADP buffer conditions. Further efforts are under way to investigate such and interesting result.