Protein dynamics. Mössbauer spectroscopy on deoxymyoglobin crystals

F. Parak, E. W. Knapp, D. Kucheida

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Abstract

Mössbauer absorption experiments on 57Fe of deoxygenated myoglobin crystals and on K4 57Fe(CN)6 dissolved in the water of metmyoglobin crystals were performed over a large temperature range. At low temperatures the mean square displacements, 〈x2〉, of the iron indicate solid-like behaviour of the whole system, whereas at higher temperatures protein-specific modes of motion contribute to 〈x2>. The protein dynamics are correlated with the mobility of the water within the protein crystals. A Brownian oscillator is used to model the protein-specific modes of motion measured at the 57Fe nucleus. Three modes are necessary for understanding the Mössbauer spectrum. Two of them correspond to an extremely overdamped Brownian oscillator. The third mode can be understood as quasi-free diffusion. Whereas the protein molecule is frozen in conformational substates in the low temperature regime, it reaches transition states with a finite probability in the high temperature regime. The surface water mediates a possible trigger mechanism that switches on protein dynamics within a narrow temperature interval. Results from Mössbauer spectroscopy and from X-ray structure analysis are compared.

Original languageEnglish
Pages (from-to)177-194
Number of pages18
JournalJournal of Molecular Biology
Volume161
Issue number1
DOIs
StatePublished - 15 Oct 1982

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