NMR structure and dynamics of monomeric neutrophil-activating peptide 2

Neutrophil-activating peptide 2 (NAP-2), which demonstrates a range of proinflammatory activities, is a 72-residue protein belonging to the alpha-chemokine family. Although NAP-2, like other alpha-chemokines, is known to self-associate into dimers and tetramers, it has been shown that the monomeric form is physiologically active. Here we investigate the solution structure of monomeric NAP-2 by multi-dimensional 1H-NMR and 15N-NMR spectroscopy and computational modelling. The NAP-2 monomer consists of an amphipathic, triple-stranded, anti-parallel beta-sheet on which is folded a C-terminal alpha-helix and an aperiodic N-terminal segment. The backbone fold is essentially the same as that found in other alpha-chemokines. 15N T1, T2 and nuclear Overhauser effects (NOEs) have been measured for backbone NH groups and used in a model free approach to calculate order parameters and conformational exchange terms that map out motions of the backbone. N-terminal residues 1 to 17 and the C-terminus are relatively highly flexible, whereas the beta-sheet domain forms the most motionally restricted part of the fold. Conformational exchange occurring on the millisecond time scale is noted at the top of the C-terminal helix and at proximal residues from beta-strands 1 and 2 and the connecting loop. Dissociation to the monomeric state is apparently responsible for increased internal mobility in NAP-2 compared with dimeric and tetrameric states in other alpha-chemokines.