Thermodynamic properties of BPTI variants with highly simplified amino acid sequences.
We report the first detailed thermodynamic analysis of simplified proteins by differential scanning calorimetry (DSC). The experiments were carried out with five simplified BPTI variants, whose structures and activities have been reported, in which several residues not essential for specifying the tertiary structure were replaced by alanine. In most aspects, the thermodynamics of simplified proteins were very similar to, if not essentially identical with, those of natural proteins. In particular, they undergo a highly cooperative two-state thermal unfolding process with a large enthalpy change, which is a thermodynamic hallmark of the native state of natural globular proteins. Furthermore, the specific enthalpy and entropy changes upon unfolding at 110 degrees C were close to values invariably observed for small natural globular proteins (55 J g(-1) and ~16 J K(-1) g(-1), respectively). On the other hand, two simplified BPTI variants, BPTI-21 and BPTI-22 (containing 21 and 22 alanine residues), were enthalpically stabilized while entropically destabilized with respect to the reference BPTI-[5,55] molecule. This peculiar type of entropy-enthalpy compensation is in sharp contrast to the usual enthalpy destabilization/entropy stabilization observed in mutational studies of natural proteins. Overall, we conclude that a thermodynamic native state can be achieved by proteins encoded with extensively simplified sequences.
Department of Biotechnology and Life Sciences, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakamachi, Koganei-shi, Tokyo 184-8588, Japan.
Atsushi
A
Kato
Munetaka
M
Yamada
Shigeyoshi
S
Nakamura
Shun-Ichi
S
Kidokoro
Yutaka
Y
Kuroda
D000595:Amino Acid Sequence; D000818:Animals; D007611:Aprotinin / Q000737:chemistry*; D002417:Cattle; D019277:Entropy; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry*; D017510:Protein Folding; D013816:Thermodynamics
D050505:Mutant Proteins; D007611:Aprotinin