A quantitative NMR spectroscopic examination of the flexibility of the C-terminal extensions of the molecular chaperones, αA- and αB-crystallin

► The C-terminal extensions of α-crystallin are flexible, polar and are involved in chaperone action. ► Flexibility of the C-terminal residues in wild type αA- and αB-crystallin increases along the C-terminal extension (i.e. away from the core of the protein). ► During chaperone action with reduced α-lactalbumin, the residues of the C-terminal extension of the chaperone show reduced flexibility and appear to be involved in a dynamic interaction with the target protein. ► Flexibility of residues in the extensions of some C-terminal mutants, I159A/I161A αB- and K175L αB-crystallin is disrupted, and this is consistent with altered structure and chaperone activity seen in previous studies.