Graduate STEM Fellow Profile

Cassandra Guarino

Project Title: CLIMB: Cornell's Learning Initiative in Medicine and Bioengineering
Thesis: Understanding N-linked glycosylation using Escherichia coli
College/University: Cornell University
Research Advisor: Matthew DeLisa
Degree Sought: Ph.D., Chemical and Biomolecular Engineering
Research Focus: Understand N-linked glycosylation in protein production power-house, E. coli, & use to produce a variety of therapeutic proteins
Teaching Partner(s): Ronald Reed

Description of Research

Our summer research project focused on the synthesis and design of carbohydrate microarrays which could be used in both diagnostic and research applications. Current methods for production of carbohydrate microarrays require expensive techniques for in-vitro carbohydrate production. Here, we proposed a method for making a carbohydrate microarray by decorating bacteriophage in-vivo with carbohydrates, specifically O-antigens originating from pathogenic bacteria. The glycophage are produced by helper phage infection of cells carrying an O-antigen operon, an oligosaccharide transferase (OST), and the gene for a phage coat protein engineered to contain an N-glycosylation site. The OST used in this study, Campylobacter jejuni pglB, can be functionally expressed in non-pathogenic Escherichia coli and can transfer O-antigens onto asparagine residues within specific N-glycosylation sites.

Example of how my research is integrated into my GK-12 experience

Most people view bacteria as pathogens that make you sick, but not all bacteria are bad. In fact, bacteria, specifically non-pathogenic E. coli, are commonly used as protein production hosts, with the capacity to survive while more than 20% of the total protein content is composed of foreign protein. Proteins such as insulin can be produced in E. coli and used for therapeutic purposes. One goal of the GK-12 experience is to use this protein production host to teach students the central dogma of molecular biology–DNA→RNA→Protein–in a way that allows them to visualize the process. Students will be challenged to design DNA coding for a fluorescent protein, and when the cells express the protein from their engineered DNA sequence, the cells will glow.