Three-dimensional structure of RK-1: A novel alpha-defensin peptide

NMR spectroscopy and simulated annealing calculations have been used to det ermine the three-dimensional structure of RK-1, an antimicrobial peptide fr om rabbit kidney recently discovered from homology screening based on the d istinctive physicochemical properties of the corticostatins/defensins. RK-1 consists of 32 residues, including six cysteines arranged into three disul fide bonds. It exhibits antimicrobial activity against Escherichia coli and activates Ca2+ channels in vitro. Through its physicochemical similarity, identical cysteine spacing, and linkage to the corticostatins/defensins, it was presumed to be a member of this family. However, RK-1 lacks both a lar ge number of arginines in the primary sequence and a high overall positive charge, which are characteristic of this family of peptides. The three-dime nsional solution structure, determined by NMR, consists of a triple-strande d antiparallel beta -sheet and a series of turns and is similar to the know n structures of other alpha -defensins. This has enabled the definitive cla ssification of RK-1 as a member of this family of antimicrobial peptides. U ltracentrifuge measurements confirmed that like rabbit neutrophil defensins , RK-1 is monomeric in solution, in contrast to human neutrophil defensins, which are dimeric.