Biology 100
Biology 191
Biology 301
Biology 494

Biophysical Basis of Stability of Proteins from Thermophilic Organisms
In my graduate research in the Molecular and Cell Biology Department at UC Berkeley, I asked the question: What makes proteins from thermophilic organisms (which live at unusually high temperatures) more stable than homologous proteins from mesophiles (moderate-temperature dwellers)?  Sequence-based and structural comparisons of thermophilic and mesophilic homologs do not reveal any obvious rules.  I used biophysical methods, such as circular dichroism, calorimetry and nuclear magnetic resonance to investigate this question at a thermodynamic level.  My research came to the surprising conclusion that the thermophilic enzyme I studied (ribonuclease H from the bacterium Thermus. thermophilus) retains a partial residual structure even when unfolded, whereas its mesophilic homolog (ribonuclease from E. coli) has the ability to denature to a completely random unfolded state.  This conclusion has implications for the understanding of how thermophilic proteins balance their high stability with the flexibility required for functioning at high temperatures.  Finely tuned balance between protein stability and flexibility might be important for survival of thermophilic organisms at high temperatures. In future research projects with Agnes Scott College students, I plan to further investigate questions related to thermostability of proteins from thermophilic bacteria.  Do other thermophilic proteins achieve high stability in a manner similar to ribonuclease H?  What can we learn about evolution of thermostability by studying sequence and structural properties of related proteins?

Therapeutically-Interesting Bacterial Proteases
As a researcher at the Celiac Sprue Research Foundation in Palo Alto, CA, I studied bacterial enzymes, which were candidates for development of enzyme-based treatment for celiac sprue.  Celiac sprue is the only autoimmune disease for which the environmental trigger has been identified.  This trigger is gluten - a set of proteins, found in wheat, barley and several other grains.  Gluten toxicity residues in proline-rich peptides, which are not cleaved by enzymes normally present in the digestive tract, but which can be cleaved by certain exogenous enzymes. 

In my research, I used biochemical and biophysical techniques to characterize bacterial proteases potentially capable of detoxifying gluten.  I plan to continue characterization of a protease from Lactobacillus helveticus in collaboration with Agnes Scott students.  This enzyme has an interesting biochemical profile, which will be examined in collaboration with Agnes Scott College students.

Robic S, Kaiser S, Jungck JR. Prion puzzle: From protein structure to mad cows. Invited module for Evolutionary Bioinformatics : Making Meaning of Molecular Messages. Manuscript in preparation.

Robic S., Gass, J., Khosla, C, Gray GM.  PEGylation leads to improved protease resistance profile of prolyl endopeptidases.  Manuscript in preparation.

Robic S, Khosla, C, Gray GM.  Biochemical characterization of Lactobacillus helveticus prolyl endopeptidase.  Manuscript in preparation.

Robic S, Guzman-Cascado M, Sanchez-Ruiz JM, Marqusee, S. 2003. Role of residual structure in the unfolded state of a thermophilic protein.  PNAS100 (20):11345-9

Guzman-Casado M, Parody-Morreale A, Robic S, Marqusee S, Sanchez-Ruiz JM.  2003.  Energetic evidence for formation of a pH-dependent hydrophobic cluster in the denatured state of T. thermophilus RNase H.  Journal of Molecular Biology 329: 731-743

Robic S, Berger JM, Marqusee S. 2002. Contributions of folding cores to the thermostabilities of two ribonucleases H.  Protein Science 11 (2): 381-389

Mallis RJ, Brazin K, Jez JM, Wilson EK, Dieckmann GR, Robic S, Harrahy J. 2001 Proteins: the complete works [Meeting review] Trends in Biochemical Sciences26:11:642-643

Jungck JR, Robic S. 2001 Topological toys, tinkering thinking: Knot theory for the three R’s of DNA [Meeting].  FASEB J 15 (4): A167-A167

Walstrom KM, Dozono JM, Robic S, et al. 1997.  Kinetics of the RNA-DNA helicase activity of Escherichia coli transcription termination factor rho 1. Characterization and analysis of the reaction.  Biochemistry- 36 (26): 7980-7992

Oral Presentations and Workshops
FASEB Protein Folding in the Cell 2002.  Vermont. USA. Selected as one of the two graduate student talks based on poster abstracts.  Are the unfolded states different in proteins from thermophilic and mesophilic organisms?

BioQUEST Summer Workshop (Systems Biology) 2004.  Beloit, WI. Participated in workshop to develop curricular materials for systems biology edication.

BioQUEST Summer Workshop (Exploring Complex Data Sets) 2006. Beloit, WI.  Led session on Teaching Protein Folding Using Software with Brain White (University of Massachusetts)

Poster Presentations
2003 Johns Hopkins Protein Folding Meeting, Berkeley Springs, WV, USA

2002 FASEB Protein Folding in the Cell 2002.  Vermont. USA

2001 Protein Society Meeting, Philadelphia, PA, USA

2000 Gibbs Protein Thermodynamics Meeting, Carbondale, IL, USA

2000 Protein Society Meeting, San Diego, CA, USA