Investigation of Aggregative Properties of the Antimicrobial Peptide LL‐37 by Dynamic Light Scattering (DLS) and Electrophoretic Shift Mobility Assay (EMSA)

Abstract

The antimicrobial peptide LL‐37 is a member the cathelicidin family of antimicrobial peptides that play a role in mammalian innate immune defense and have potential for combating bacterial infection and antibiotic resistance. LL‐37 is known to induce cell death by disrupting the cell membrane, but the mechanism for membrane disruption is still unknown. By studying peptide properties, such as aggregation, we may better understand how LL‐37 induces cell death. We have used dynamic light scattering (DLS) and electrophoretic mobility shift assays (EMSA) to investigate the aggregative properties of LL‐37. DLS monitors diffusion and thus the hydrodynamic radius of scattering centers by analyzing temporal fluctuations in scattered light intensity using the autocorrelation technique. In the concentration range of 150 to 37 μM, we observe by DLS that LL‐37 shows decreasing mobility as concentration increases, indicative of particle size transition from a hydrodynamic radius on the order of 1 to 1,000 nm. EMSA with peptide detection by western blotting provides information about aggregate size at lower concentrations, ranging from 0.8 to 50 μM. As a result, the particle size distribution shifts decisively in favor of relatively small aggregates as the concentration falls below 50 μM, indicated by the decrease in hydrodynamic radius in DLS and increased protein migration in EMSA.