Solution studies of chymotrypsin inhibitor-2 glutamine insertion mutants show no interglutamine interactions

Mutants of chymotrypsin inhibitor protein 2 have previously been studied in which 4 or 10 glutamine residues were inserted into the inhibitory loop of the protein between residues 59 and 60, as potential models for the behavi our of glutamine tracts in proteins associated with polyglutamine-expansion neurodegenarative diseases. These mutants form very stable monomers, dimer s and trimers. Although the cause of oligomerisation was found to be domain -swapping, it was thought that the glutamine insertions might nevertheless show evidence of weak interglutamine interactions in solution that could mi mic those occurring in disease-associated proteins. In the present NMR stud y, we used steady-state N-15{H-1} NOE measurements and chemical shift compa risons to characterise the motional properties of the inserted glutamines i n these CI2 mutants. We found the glutamines to be highly mobile, with no e vidence of interactions amongst them in either monomers or dimers, (C) 2001 Academic Press.