Solution structure of a protein inhibitor of neuronal nitric oxide synthase.

The structure of the neuronal nitric oxide synthase inhibitory protein, PIN (protein inhibitor of nNOS), has been determined by NMR spectroscopy. Two N-terminal antiparallel alpha-helices pack against a four-stranded antiparallel beta-sheet in the C-terminal region of the protein, forming a two-layer alpha/beta plait. The three dimensional structure of PIN resembles the fold of the B-chain of aspartylglucosaminidase. A non-prolyl cis peptide bond was found between Pro 52 and Thr 53 of the protein. PIN has a large solvent-exposed hydrophobic surface that contains a cavity and is rimmed with positive charges. This surface may serve as the primary target-binding region for this multi-functional regulatory protein.