Poster abstracts

Poster number 121 submitted by Jason Lavinder

Combinatorial biophysics: Library approaches to hydrophobic core repacking of the four-helix bundle protein Rop

Jason J. Lavinder (Ohio State Biochemistry Program, The Ohio State University), Sanjay B. Hari (Department of Biochemistry, The Ohio State University), Thomas J. Magliery (Department of Chemistry and Ohio State Biochemistry Program, The Ohio State University)

Abstract:
The inability to accurately decipher the relationship between protein sequence and structural stability presents a major difficulty in predicting the effects of mutation on protein folding. We are analyzing this complicated relationship using rigorous high-throughput methods to explicitly test hypotheses that have been generated by previous de novo design studies and offer a more complete understanding of protein folding and structure. Our studies focus on the sequence-stability-function relationship of the four-helix bundle protein Rop through the means of combinatorial repacking of the hydrophobic core. Using a novel in vivo screen that utilizes GFP as a reporting phenotype, we are able to screen large libraries for functional variants, representing Rop mutants that are able to achieve a native-like fold. These functional variants from the repacked libraries have been sequenced via high-throughput colony sequencing technology to accumulate a data set that is significantly large to produce statistically significant sequence sampling. The final data set has been statistically analyzed in a variety of fashions to understand the correlation and context of hydrophobic core packing. To gain insight into the thermodynamic consequences of sequence on structural stability, we have developed a high-throughput calorimetry (HTC) assay to assess the relative stabilities of the sequenced active variants (as well as a set of inactive variants for comparative analysis). Using this HTC assay, the thermal unfolding of the variants can be measured in real-time 96-well format. This is the most comprehensive study to date to collect detailed thermodynamic information on a single protein’s sequence-stability relationship. The HTC assay represents novel technology development that allows high-throughput thermodynamic measurements to be made on combinatorially engineered proteins. Select Rop variants from the libraries are being biophysically characterized via circular dichroism spectroscopy, thermal and chemical denaturation studies, HSQC NMR, and, in certain cases, X-ray crystallographic techniques. This will aid in validating structural hypotheses that are generated from the high-throughput studies and allow conclusions to be drawn on sequence-stability patterns that emerge.

Keywords: protein design, protein folding