Dynamic light scattering (DLS) is an instrumental technique used to measure the size of nanoparticles and biological macromolecules, such as proteins. The technique utilizes Brownian motion, the random movement of particles due to collisions with solvent molecules. As light from a laser hits these moving particles, the intensity of light that hits the detector fluctuates. Smaller particles diffuse faster in solution, leading to greater intensity fluctuations, while larger particles diffuse slower in solution, leading to smaller intensity fluctuations. These fluctuations are mathematically analyzed by the instrument to generate information about particle size, displayed as "peaks" on a particle size by distribution (PSD) graph.
Metacaspases are cysteine protease enzymes that require calcium to cleave other proteins. They specifically cleave after positively charged amino acid residues such as arginine and lysine. Metacaspases can also cleave themselves in a process called autoproteolysis. Our lab studies the Type Ia metacaspases found in the fungal species Schizophyllum commune (ScMCA-Ia). We hypothesize that when ScMCA-Ia cleaves itself, the enzyme either stays intact or separates into two polypeptide chains. To test this hypothesis, we employed DLS instrumentation. Theoretically, if the enzyme stays intact, one peak would be seen on the PSD graph; if the enzyme is separated, two peaks would be seen on the PSD graph. Preliminary results show that one peak is observed as well as a shift in particle size. Native (not cleaved) metacaspase is 90 nm, and upon autoproteolytic cleavage, the enzyme unfolds slightly to afford a peak at 110 nm. Future studies should improve on the replicability of this technique for analyzing ScMCA-Ia metacaspases using DLS.