Structure-Function Relationships of Food-Related Proteins/Enzymes: Aspartic Proteinases

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The long-term goal of our NSERC funded research program has been to elucidate and refine the nature of structure-function relationships (SFRs) of food-related proteins (particularly enzymes) at a fundamental, molecular level. Our work focuses on aspartic proteinases (APs), the Peptidase A1 family of enzymes. While most APs conform to certain characteristics (optimum pH for activity, mechanism of action, structural similarity), there are differences (stability, target preference, post-translational modification, biological function) that make APs an excellent model for SFR studies. In the food area, APs play prominent roles as processing aids in the manufacture of a variety of products, e.g., chymosin is used to coagulate milk in the production of cheese. Additionally, APs are part of food plant protection (e.g., barley, tomato, potato), and some are active against food pathogens (e.g., toxic Bacillus and Staphylococcus species). Thus, APs are critical to food safety and supply. Understanding the biochemistry of APs is not only important for food-related processes/issues, but AP SFR knowledge is also relevant in metabolic functions (regulating blood pressure) and in disease states (malaria, AIDS). The proposed research will continue to examine SFRs of APs using a combination of protein engineering and physicochemical techniques to contribute to the current state of knowledge in the three principal areas of (I) protein folding processes, (II) plant AP anti-pathogen domain SFRs, and (III) the similarity/dissimilarity of APs from varied sources. Protein folding will be studied by determining how particular AP portions termed prosegments affect protein folding/unfolding. Anti-pathogen AP domains will be investigated in terms of their interactions with membranes as well as their roles for AP enzymatic functioning. Studying the similarity/dissimilarity of APs will be centred on APs that display extreme behaviour including functioning at high temperatures as well as enzyme stability at unusual pH values. By answering fundamental, hypothesis-driven questions, these studies will undoubtedly aid in the more efficient use, control and design of food-related proteins/enzymes with desired functions.