Microscopic_Mechanism_Cold_Denaturation_PRL_100_118101_Dias(2..8)

Microscopic_Mechanism_Cold_Denaturation_PRL_100_118101_Dias(2..8)

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Microscopic Mechanism for Cold Denaturation Cristiano L. Dias, 1 Tapio Ala-Nissila, 2,3 Mikko Karttunen, 4 Ilpo Vattulainen, 5,6,7 and Martin Grant 1 1 Physics Department, Rutherford Building, McGill University, 3600 rue University, Montre ´al, Que ´bec, Canada H3A 2T8 2 Department of Physics, Brown University, Providence, Rhode Island 02912-1843, USA 3 Department of Engineering Physics, Helsinki University of Technology, P.O. Box 1100, FI-02015 TKK, Espoo, Finland 4 Department of Applied Mathematics, The University of Western Ontario, London, Ontario, Canada 5 Institute of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland 6 MEMPHYS–Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark 7 Helsinki Institute of Physics, Helsinki University of Technology, Helsinki, Finland (Received 20 April 2007; published 18 March 2008) We elucidate the mechanism of cold denaturation through constant-pressure simulations for a model of hydrophobic molecules in an explicit solvent. We Fnd that the temperature dependence of the hydrophobic effect induces, facilitates, and is the driving force for cold denaturation. The physical mechanism underlying this phenomenon is identiFed as the destabilization of hydrophobic contact in favor of solvent-separated conFgurations, the same mechanism seen in pressure-induced denaturation. A phe- nomenological explanation proposed for the mechanism is suggested as being responsible for cold denaturation in real proteins. DOI: 10.1103/PhysRevLett.100.118101 PACS numbers: 87.14.E ÿ , 87.15. ÿ v, 87.15.A ÿ , 87.15.B ÿ Under physiological conditions, proteins adopt a unique three-dimensional (3D) structure [ 1 ]. This structure is maximally stable at about 17 ± C and becomes unstable at both high ( ² 60 ± C ) and low ( ÿ 20 ± C ) temperatures [ 2 4 ]. The latter phenomenon, where the protein unfolds thereby increasing its entropy, is called cold denaturation and is accompanied by a decrease in the entropy of the entire system. This counterintuitive behavior has been experi- mentally veriFed [ 3 , 5 ] but has remained a subject of con- troversy [ 2 , 4 ], since a satisfactory microscopic explanation for this phenomenon has not yet emerged. Resolving cold denaturation microscopically would facilitate understand- ing the forces responsible for the structure of proteins and, in particular, the role of the complex hydrophobic effect. In the case of diluted proteins, hydrophobicity is con- sidered the main driving force for folding and unfolding [ 6 ]. Consequently, cold denaturation has been studied us- ing explicit models that take hydrophobicity into account [ 7 10 ]. One class of such models [ 7 , 9 ] associates the phenomena with the different energetic states of shell water, i.e., water molecules neighboring the protein, in a lattice. A more realistic water model [ 8 ] supports this view, as water-water hydrogen bonding among shell water has been found to increase at low temperatures and to correlate with cold denaturation. Meanwhile, another class of mod- els suggests that the density ±uctuations of water are responsible for cold denaturation [ 11 , 12 ]. Despite the
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This note was uploaded on 07/20/2011 for the course EMA 6165 taught by Professor Brennan during the Spring '08 term at University of Florida.

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Microscopic_Mechanism_Cold_Denaturation_PRL_100_118101_Dias(2..8)

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