The conformation of substance P in lipid environments

NMR and CD studies have been used to analyze the model membrane-bound structure of the neuropeptide substance P (RPKPQQFFGLM-NH2, SP), which has previously been proposed as the NK1 receptor active form. Conformations were determined for the SP in the presence of aqueous solutions of zwitterionic dodecylphosphocholine (DPC) and anionic sodium dodecylsulfate (SDS) micelles. The two structures are similar, although fast exchange between free and bound forms was observed for SP with DPC micelles, and predominantly bound characteristics were found for SP in SDS. The addition of 150-200 mM NaCl had no observable effect on the bound conformation in either case. Thus, the structure of SP at a micelle surface is determined largely by hydrophobic forces, and the electrostatic interactions determine the amount of SP that is bound.