Multidimensional heteronuclear NMR has been applied to the structural analysis of
myotrophin, a novel
protein identified from spontaneously hypertensive rat hearts and hypertrophic human hearts.
Myotrophin has been shown to stimulate
protein synthesis in myocytes and likely plays an important role in the initiation of
cardiac hypertrophy, a major cause of mortality in humans. Recent
cDNA cloning revealed that
myotrophin has 11B
amino acids containing 2.5 contiguous ANK repeats, a motif known to be involved in a wide range of macromolecular recognition. A series of two- and three-dimensional heteronuclear bond correlation NMR experiments have been performed on uniformly 15N-labeled or uniformly 15N/13C-labeled
protein to obtain the 1H, 15N, and 13C chemical shift assignments. The secondary structure of
myotrophin has been determined by a combination of NOEs, NH exchange data, 3JHN alpha coupling constants, and chemical shifts of 1H alpha, 13C alpha, and 13 C beta. The
protein has been found to consist of seven helices, all connected by turns or loops. Six of the seven helices (all but the C-terminal helix) form three separate helix-turn-helix motifs. The two full ANK repeats in
myotrophin are characteristic of multiple turns followed by a helix-turn-helix motif. A hairpin-like turn involving L32-R36 in ANK repeat #1 exhibits slow conformational averaging on the NMR time scale and appears dynamically different from the corresponding region (D65-169) of ANK repeat #2.