Osmolytes as modulators of conformational changes in serpins

Protein misfolding and aggregation play an integral role in many diseases. The misfolding of the serpin (SERine Proteinase INhibitor) alpha (1)-antitrypsin results in the accumulation of insoluble polymers within hepatocytes and alpha (1)-antitrypsin deficiency in plasma, predisposing patients to liver cirrhosis and emphysema. We have examined the effect of three naturally occurring osmolytes, sarcosine, glycine betaine and trimethylamine N-oxide, on conformational changes in alpha (1)-antitrypsin. All three solutes protected native al-antitrypsin against thermally induced polymerisation and inactivation in a concentration-dependent manner Further spectroscopic analysis showed that sarcosine stabilises the native conformation of alpha (1)-antitrypsin, thus hindering its conversion to an intermediate state and subsequent polymerisation. On refolding in the presence of sarcosine, alpha (1)-antitrypsin formed a heterogeneous population, with increasing proportions of molecules adopting an inactive conformation in higher concentrations of the osmolyte. These data show that sarcosine can be used to prevent abnormal structural changes in native alpha (1)-antitrypsin, but is ineffective in facilitating the correct folding of the protein. The implications of these results in the context of conformational changes and states adopted by al-antitrypsin are discussed.