SOLUTION STRUCTURE OF BOVINE NEUTROPHIL BETA-DEFENSIN-12 - THE PEPTIDE FOLD OF THE BETA-DEFENSINS IS IDENTICAL TO THAT OF THE CLASSICAL DEFENSINS

The solution structure is reported for bovine neutrophil beta-defensin -12 (BNBD-12), a member of the beta-defensin family of antimicrobial p eptides. Structural constraints in the;form of proton-proton distances , dihedral angles, and hydrogen bond constraints were derived from two -dimensional, homonuclear magnetic resonance spectroscopy experiments. The three-dimensional structure of BNBD-12 was calculated using dista nce geometry and restrained molecular dynamics. An ensemble of structu res with low NOE constraint violation energies revealed a precisely de fined triple-stranded, antiparallel beta-sheet as the structural core of the peptide. The N-terminal beta-strand and three locally well-defi ned tight turns form a hydrophobic face. Conserved isoleucine and glyc ine residues form a beta-bulge structure which initiates a beta-hairpi n secondary structure motif composed of the second and C-terminal beta -strands. The beta-hairpin contains numerous charged residues and form s the cationic face of BNBD-12. The N-terminal residues were found to be disordered, due to an absence of tertiary NOEs. The triple-stranded beta-sheet, the beta-bulge preceding the hairpin, and the cationic/hy drophobic amphiphilic character are definitive features of all defensi n structures determined to date. Further, we predict that the tracheal antimicrobial peptide (TAP) and the recently described gallinacins wi ll have tertiary structures similar to that of BNBD-12.