Portrayal of Complex Dynamic Properties of Sugarcane Defensin 5 by NMR: Multiple Motions Associated with Membrane Interaction

Defensins are essentially ancient natural antibiotics with potent activity extending from lower organisms to humans. Sd5 is a recently described antifungal defensin that appears to be the result of a recent gain of function. We reported here the solution NMR structure of Sd5 and characterized the backbone dynamics in the free state and in the presence of membrane models. N-15 relaxation dispersion measurements indicate intrinsic conformational exchange processes, showing two clear distinct k(ex), 490 and 1800 s(-1). These multiple motions may be related to transient twisting or breathing of the alpha helix and beta sheet. The stages of membrane recognition and disruption by Sd5 over a large timescale range were mapped and demonstrated that Sd5 in solution sampled an ensemble of different conformations, of which a subset is selected upon membrane binding. Defensins share similar structures, but we demonstrated here that their dynamics can be extremely diverse.