Structure Function of Food Related Proteins

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The long-term goal of our NSERC-funded research program has been to understand the fundamental processes that explain how protein functionality is dictated by protein structure. In food systems, proteins (including enzymes) have prominent roles in texture, flavour, odour, nutrition and prophylaxis in food safety/plant pathology (e.g., antimicrobial and plant defense proteins) as well as being processing aids (e.g., chymosin coagulates milk in cheese production). The research focus of this proposal is on a group of enzymes called aspartic proteases which share highly similar structures and modes of action, that are best represented by the stomach enzyme pepsin. Despite this uniformity, a wide spectrum of different functions exist making them an ideal model to study how protein structure determines function. Building on previous research by our group and others, the proposed research program addresses fundamental knowledge gaps in two overarching areas: 1) food spoilage-related bioactive protein segments of aspartic proteases in plants; and 2) the underpinnings of aspartic protease structure tolerance to heat and alkalinity, and selectivity for particular targets. For the first research area, aspartic proteases from plants have an extra portion compared to those from non-plant sources called the plant-specific insert (PSI). The PSI is critical for plant aspartic proteases to interact with membranes, including activity against plant pathogens as part of plants’ immune responses to invading fungi. The structure and specific points of contact with membranes will be solved at the highest level of molecular detail in order to better understand the mode of action of the PSI. The second research area will entail solving the structures of a little-studied malarial aspartic protease (plasmepsin V) complexed with well-known inhibitors to narrow the possible range of binding sites, so as to direct computer-aided inhibitor design specific to plasmepsin V. Other studies will contribute to understanding how atypical aspartic proteases are able to work at extreme temperature (thermopsin from an organism found in acidic hot springs) and non-acidic pH (renin from human kidney). Thermopsin and renin will serve as templates for engineering pepsin (which is not temperature- or neutral pH-stable) by providing a means of testing the stabilizing effects of key structural features. The impact of the proposed research program will be to improve knowledge regarding AP structures and functions thereby enabling novel strategies for interventions in food-related challenges such as plant diseases and enzyme biotechnological applications.