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2009, 113, 5001–5006 Published on Web 03/26/2009
Proteins Remain Soft at Lower Temperatures under Pressure Xiang-qiang Chu,† Antonio Faraone,‡,§ Chansoo Kim,†,| Emiliano Fratini,⊥ Piero Baglioni,⊥ Juscelino B. Leao,‡ and Sow-Hsin Chen*,† Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Computational Science Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, Korea, NIST Center for Neutron Research, Gaithersburg, Maryland 20899-8562, Department of Material Science and Engineering, UniVersity of Maryland, College Park, Maryland 20742, and Department of Chemistry and CSGI, UniVersity of Florence, Sesto F.no, Florence, I-50019 ReceiVed: January 19, 2009; ReVised Manuscript ReceiVed: March 10, 2009
The low-temperature behavior of proteins under high pressure is not as extensively investigated as that at ambient pressure. In this paper, we study the dynamics of a hydrated protein under moderately high pressures at low temperatures using the quasielastic neutron scattering method. We show that when applying pressure to the protein-water system, the dynamics of the protein hydration water does not slow down but becomes faster instead. The degree of “softness” of the protein, which is intimately related to the enzymatic activity of the protein, shows the same trend as its hydration water as a function of temperature at different pressures. These two results taken together suggest that at lower temperatures, the protein remains soft and active under pressure. It is well-known that some bacteria can survive under extremely high pressure and low temperature in the deep ocean. The microorganisms living in the deepest ocean, yet isolated and characterized, were sampled at 11000 m depth or 1100 bar in the deep-sea sediments of the Marianas trench, where the Pacific oceanic lithosphere subducts into the Earth’s mantle.1 How can proteins in the microorganisms still function under these extreme conditions? Besides the fact that high pressure denatures most of the dissolved proteins above 3000 bar, the behaviors of proteins under pressures below the denaturation limit (
