Conformational stabilities of the rat alpha- and beta-parvalbumins

It is widely believed that beta-parvalbumin (PV) isoforms are intrinsically less stable than alpha-parralbumins, due to greater electrostatic repulsio n and an abbreviated C-terminal helix, However, when examined by differenti al scanning calorimetry, the ape-form of the rat beta-PV (i,e, oncomodulin) actually displays greater thermal stability than the alpha-PV, Whereas the melting temperature of the alpha isoform is 45.8 degrees C at physiologica l pH and ionic strength, the T-m for the beta isoform is more than 7 degree s higher (53.6 degrees C). This result suggests that factors besides net ch arge and C-terminal helix length strongly influence parvalbumin conformatio nal stability. Extension of the F helix in the beta-PV, by insertion of Ser -109, has a modest stabilizing effect, raising the T-m by 1.10, Truncation of the alpha-PV F helix, by removal of Glu-108, has a more profound impact, lowering the T-m by 4.0 degrees, (C) 1999 Federation of European Biochemic al Societies.