(742f) Structure and Dynamics of Human Beta Defensin Interacting with Bacterial Lipid Membranes

Human Beta Defensins (hBD) are antimicrobial peptides which are produced as a first line of defense by all multicellular organisms. These proteins have broad activities to directly kill bacteria, yeast, fungi, viruses and even cancer cells. hBD has 6 family members, from hBD type 1 (hBD-1) to type 6 (hBD-6). They have distinct antibacterial activities although sharing similar structures. In this research, human beta defensin type 1 (hBD-1) and type 3 (hBD-3) are studied in order to acquire a better understanding of the structures and dynamics of both proteins. The difference between hBD-1 and hBD-3 is mainly the number of residues, their charges and their salt sensitive matter. hBD-1 has 36 residues with a change of positive 4 and acts in salt sensitive matter while hBD-3 has 45 residues with a charge of positive 11 and acts in salt insensitive matter. However, what they have in common are 3 pairs of disulfide bonds.

Firstly, we set up simulations on hBD-3 monomer and hBD-1 dimer binding with both gram-positive and gram-negative bacterial lipid membranes with CHARMM-GUI software and ran for at least 50 ns each in wildtype form by using NAMD program and CHARMM forcefields. The compositions of Gram-positive and Gram-negative bacterial lipid membranes that were used to set up the simulations consist of 4 types of lipids: palmitoyloleoyl phosphatidylglycerol (POPG), palmitoyloleoyl phosphatidylethanolamine (POPE), 1,2-dioleoyal-3-trimethylammonium-propane (DOTAP) and tetraoleyl cardiolipin (TOCL), with different molar ratios. The Gram-positive lipid membrane was set up with 60% POPG, 14% POPE, 15% DOTAP and 10% TOCL. Gram-negative lipid membrane was set up with 20% POPG, 70% POPE, and 10% TOCL. Then we analyzed hBD on the bacterial membrane simulation trajectories by calculating Root Mean Square Deviation (RMSD), Root mean square fluctuation (RMSF), the number of hydrogen bonds of hBD-1 and hBD-3 with lipids using VMD program.

It is found that hBD-1 has more structure change than hBD-3. It is also found that hBD-3 forms more hydrogen bonds with the Gram-negative and Gram-positive membranes than those of hBD-1, and hBD-3 has more stable binding on bacterial membranes than hBD-1. The result can help to explain the binding and activity discrepancy of hBDs during bacterial eliminating.