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Publication Abstract from PubMed

We report a thermodynamic and structural analysis of six extensively simplified bovine pancreatic trypsin inhibitor (BPTI) variants containing 19-24 alanines out of 58 residues. Differential scanning calorimetry indicated a two-state thermal unfolding, typical of a native protein with densely packed interior. Surprisingly, increasing the number of alanines induced enthalpy stabilization, which was however over-compensated by entropy destabilization. X-ray crystallography indicated that the alanine substitutions caused the recruitment of novel water molecules facilitating the formation of protein-water hydrogen bonds and improving the hydration shells around the alanine's methyl groups, both of which presumably contributed to enthalpy stabilization. There was a strong correlation between the number of water molecules and the thermodynamic parameters. Overall, our results demonstrate that, in contrast to our initial expectation, a protein sequence in which over 40% of the residues are alanines can retain a densely packed structure and undergo thermal denaturation with a large enthalpy change, mainly contributed by hydration.

Crystal structures of highly simplified BPTIs provide insights into hydration-driven increase of unfolding enthalpy.,Islam MM, Yohda M, Kidokoro SI, Kuroda Y Sci Rep. 2017 Mar 7;7:41205. doi: 10.1038/srep41205. PMID:28266637^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.