CAREER: A Novel Twist in Nature; Proteins with a Pierced Lasso Topology

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With support from the Chemistry of Life Processes Program in the Chemistry Division and the Established Program to Stimulate Competitive Research (EPSCoR), Ellinor Haglund from the University of Hawaii is investigating a newly identified protein structure called the Pierced Lasso Topology (PLT). Proteins are sometimes called the “workhorses” in biology because they catalytically mediate the majority of chemical functions in a living cell. The breadth of these functions depends on the variety of three-dimensional shapes adopted by the chain of amino acids that make up proteins. The trace of a protein chain through space is called its topology. In a PLT, one end of the amino acid chain threads through a loop or lasso that is formed somewhere along the chain. This topology is similar to that of a simple overhand knot of a string or a rope. The chemical bond that forms the lasso can be made or broken, depending on the chemical environment of the system, and thus acts like an on/off switch for biological activity. Dr. Haglund will combine theoretical and biochemical studies with genetic experiments using fruit flies in order to investigate how PLTs can act as molecular switches to control biological activity through changes in the environment within cells. This project will be integrated with an outreach program to teach students and non-scientists how topologies seen in biology are connected with the topology of knots found in everyday life and in Polynesian culture. This research project aims to unravel functional insight for proteins with complex topologies, i.e., proteins with a pierced lasso topology (PLT). PLTs are threaded “knot-like” topologies wherein part of the chain pierces through a covalent loop. Interestingly, PLTs have been found to exist in 18% of all disulfide-containing proteins. Despite this large number, a connection between topology and biological function has not yet been established. As the first research group explicitly focusing on PLTs, the Haglund group will use biochemistry, cell biology, and biophysics tools to investigate functional consequences of disulfide chemistry in vivo and the possible role of disulfides as molecular switches to control biological activity. Molecular dynamics simulations, in vitro, and in vivo physiological assays using Drosophila melanogaster as a genetic model will be employed to examine the biological role of PLTs. This project sets out to reveal mechanistic details of how PLT proteins can fold and thread to reach their biologically active states. These studies will focus on three selected proteins (leptin, superoxide dismutase from Mycobacterium tuberculosis, and the chemokine CXCL5) that are involved in cell regulation, growth, and cell migration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.