Assistant Professor Sarah Perry of the Chemical Engineering Department at the University of Massachusetts Amherst has received a $657,920 grant from the prestigious National Science Foundation (NSF) Faculty Early Career Development (CAREER) Program to study a groundbreaking new approach to protein stabilization based on nature-inspired strategies. Her NSF research has the ultimate goal of boosting the accessibility of vaccines and other therapeutics, especially in developing countries, and extending the reach of temperature-stable proteins to sensing and catalysis applications.
As Perry explains, “Formulations of vaccines or biologics come as solutions of protein in water. In this sense, the material has more in common with a glass of milk than the inside of a cell. This analogy continues in that most purified proteins and vaccine formulations are extremely sensitive to temperature and must be kept refrigerated.”
In fact, Perry continues, the need to maintain refrigeration during the storage and transportation of these vaccines represents a tremendous expense and logistical challenge for both doctors and patients.
“Imagine if buying a gallon of milk meant that you had to come to the store with a cooler of ice and carry that cooler around the store with you as you did your other shopping,” says Perry. “Not only would that be more complicated and tiring, but the cooler itself would limit the amount of milk that you could buy.”
While this analogy conveys the challenge of transporting vaccines that merely have to be administered once, as Perry says, the challenge of maintaining this “cold chain” becomes even more daunting for people who have to take daily doses of temperature-sensitive biologics.
“Imagine the difficulty of planning vacation trips,” Perry observes. “What happens if a flight is delayed? How would you know if the temperature in the cooler is still acceptable? Are you willing to take that chance?”
In living tissues, proteins and enzymes perform a wide range of functions for long periods of time and at body temperatures. Perry’s research explores the idea of creating materials that are more like the interior of a cell and would therefore improve the temperature stability of vaccines and biologics by allowing them to exist in a more natural environment.
In particular, Perry looks to recreate both the “physical crowding” and the idealized chemical interactions present in the material environment of the cell. These two factors are important in controlling protein stability as the function of a protein is linked to its structure. If a protein becomes distorted or unfolds, it no longer works properly.
According to Perry, the idea of physical crowding is very straightforward in that you simply do not allow the protein enough space to unfold. However, simple crowding is not sufficient to stabilize proteins. “In addition to crowding,” she says, “our project looks to control the chemical environment surrounding proteins. Think of the chemical environment as a molecular analogy for the people around you. It is one thing to be packed into a crowded subway car with people you do not know, but it is an entirely different experience to crowd into a dance club with your friends.”
Perry adds that “This CAREER project will pioneer a new approach to protein stabilization, using a biomaterial platform to mimic the crowded, protein-rich, intracellular environment and enable the intelligent design of stabilizing formulations.”
To do so, Perry’s lab is using polymers that self-assemble into liquid-liquid, phase-separated, complex, coacervate droplets and can be used to encapsulate proteins. The concentration of polymer in these droplets is similar to the level of crowding in cells. Perry’s hypothesis is that patterns of charge, hydrophobicity, and hydrogen-bonding groups along these polymers can be used to tune the material properties, and thus the ability of these coacervates to stabilize proteins.
Perry will begin by quantifying the incorporation of model enzymes based on the material environment, theorizing that, as she says, “synergistic patterns of charge, hydrophobicity, and hydrogen-bonding groups can be used to selectively incorporate proteins into complex coacervates.”
In particular, Perry says she is looking to systematically examine how the patterns of chemistry present on both the polymeric species and on the surface of the proteins affect incorporation. This work will explore different variants of catalytically inactive caspases (protein cleaving enzymes playing vital roles in programmed cell death or inflammation), inspired by the work of Professor Jeanne Hardy and her lab in the UMass Department of Chemistry.
Finally, Perry will quantify the stabilization of catalytically active versions of caspases based on their material environment and on the premise that synthetic environments presenting patterns of charge, hydrophobicity, and hydrogen bonding groups will increase the stability of encapsulated proteins.
This NSF CAREER project is very much in keeping with the ongoing research of the Perry Research Group.
As Perry explains, “My research utilizes self-assembly, molecular design, and microfluidic technologies to generate biologically relevant microenvironments for the study and application of biomacromolecules. Individually, microfluidics represents an enabling technology for complex experiments, while control over molecular interactions in self-assembling polymer/protein systems can be used to examine the interplay between biomacromolecules and the intracellular environment.”
Perry concludes that “Together, these capabilities can be coupled to generate artificial organelle-like structures for use in applications ranging from biochemistry to bioenergetics, biocatalysis, and biomedicine. Furthermore, this work has tremendous pedagogical potential to inspire students to work at the intersection of chemistry, biology, and engineering.” (March 2020)