Rescue of the neuroblastoma mutant of the human nucleoside diphosphate kinase A/nm23-H1 by the natural osmolyte trimethylamine-N-oxide

The point mutation S120G in human nucleoside diphosphate kinase A, identified in patients with neuroblastoma, causes a protein folding defect. The urea-unfolded protein cannot refold in vitro, and accumulates as a molten globule folding intermediate. We show here that the trimethylamine-N-oxide (TMAO) corrects the folding defect and stimulated subunit association. TMAO also substantially increased the stability to denaturation by urea of both wild-type and S120G mutant. A non-native folding intermediate accumulated in the presence of 4.5–7 M urea and of 2 M TMAO. It was inactive, monomeric, contained some secondary structure but no tertiary structure and displayed a remarkable stability to denaturation.