STRUCTURE AND FUNCTION OF THE GROUP III CHAPERONINS, A UNIQUE CLADE OF PROTEIN FOLDING NANOMACHINES

The survival and descent of cells is universally dependent on maintaining their proteins in a properly folded condition. It is widely accepted that the information for the folding of the nascent polypeptide chain into a native protein is encrypted in the amino acid sequence, and the Nobel Laureate Christian Anfinsen was the first to demonstrate that a protein could spontaneously refold after complete unfolding. However, it became clear that the observed folding rates for many proteins were much slower than rates estimated in vivo. This led to the recognition of required protein-protein interactions that promote proper folding. A unique group of proteins, the molecular chaperones, are responsible for maintaining protein homeostasis during normal growth as well as stress conditions. Chaperonins (CPNs) are ubiquitous and essential chaperones. They form ATP-dependent, hollow complexes that encapsulate polypeptides in two back-to-back stacked multisubunit rings, facilitating protein folding through highly cooperative allosteric articulation. CPNs are usually classified into Group I and Group II. Here, I report the characterization of a novel CPN belonging to a third Group, recently discovered in bacteria. Group III CPNs have close phylogenetic association to the Group II CPNs found in Archaea and Eukarya, and may be a relic of the Last Common Ancestor of the CPN family. The gene encoding the Group III CPN from Carboxydothermus hydrogenoformans and Candidatus Desulforudis audaxviator was cloned in E. coli and overexpressed in order to both characterize the protein and to demonstrate its ability to function as an ATPase chaperone. The opening and closing cycle of the Chy chaperonin was examined via site-directed mutations affecting the ATP binding site at R155. To relate the mutational analysis to the structure of the CPN, the crystal structure of both the AMP-PNP (an ATP analogue) and ADP bound forms were obtained in collaboration with Sun-Shin Cha in Seoul, South Korea. The ADP and ATP binding site substitutions resulted in frozen forms of the structures in open and closed conformations. From this, mutants were designed to validate hypotheses regarding key ATP interacting sites as well as important stabilizing interactions, and to observe the physical properties of the resulting complexes by calorimetry.

TAKING THE PERSPECTIVE OF A SELLER AND A BUYER: IMPLICATIONS FOR PRICE ELICITATION AND PRICE FRAMING

This dissertation consists of two essays which investigate how assuming the role of a seller or a buyer affects valuations in a price elicitation task (essay I) and how different presentations of an equivalent price affect evaluations when a consumer plays the dual roles of a buyer and a seller in transactions involving trade-ins (essay II). Sellers’ willingness to accept (WTA) to give up a good is typically higher than buyers' willingness to pay (WTP) to obtain the good. Essay I proposes that valuation processes of sellers and buyers are guided by a motivational orientation of “getting the best.” For a seller (buyer) indicating WTA (WTP), getting the best implies receiving as much as possible to give up a specific good (giving up as little as possible to get the specific good). Results of six studies suggest that the WTA-WTP elicitation task activates different directional goals, leading to the WTA-WTP disparity. The different directional goals lead sellers and buyers to focus on different aspects and bias their cognitive reasoning and interpretation of information. By connecting the valuation process to the general motivation of getting the best, this research provides a unifying framework to explain the disparate interpretations of the WTA-WTP disparity. Many new purchases and replacement decisions involve consumers’ trading in their old products. In such transactions, the overall exchange may be priced either as separate transactions (partitioned) with price tags for the payment and the receipt or as a single net price (consolidated) which takes into account the value of the trade-in. Essay II examines whether consumers prefer a partitioned price versus a consolidated price presentation. The findings suggest that when consumers are trading in a product which has a low value relative to the price of a new product, they prefer a consolidated price. In contrast, when trading in a product which has high value, they prefer a partitioned price. The results suggest that consumers use the price of the new product as an anchor to evaluate the trade-in value, and the perception of the trade-in value influences the overall evaluation especially when the transaction is partitioned.