Abstract:
:Two-dimensional 1H NMR spectroscopy over a range of temperature through thermal unfolding has been applied to the low-spin, ferric cyanide complex of myoglobin from Aplysia limacina to search for intermediates in the unfolding and to characterize the effect of temperature on the magnetic properties and electronic structure of the heme iron. The observation of strictly linear behavior from 5 to 80 C degrees through the unfolding transition for all hyperfine-shifted resonances indicates the absence of significant populations of intermediate states to the cooperative unfolding with Tm approximately 80 degrees C. The magnetic anisotropies and orientation of the magnetic axes for the complete range of temperatures were also determined for the complex. The anisotropies have very similar magnitudes, and exhibit the expected characteristic temperature dependence, previously observed in the isoelectronic sperm whale myoglobin complex. In contrast to sperm whale Mb, where the orientation of the magnetic axis was completely temperature-independent, the tilt of the major magnetic axis, which correlates with the Fe-CN tilt, decreases at high temperature in Aplysia limacina Mb, indicating a molecular structure that is conserved with temperature, although more plastic than that of sperm whale Mb. The pattern of contact shifts reflects a conserved Fe-His(F8) bond and pi-spin delocalization into the heme, as expected for the orientation of the axial His imidazole.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Xia Z,Nguyen BD,Brunori M,Cutruzzolà F,La Mar GNdoi
10.1529/biophysj.105.062398subject
Has Abstractpub_date
2005-12-01 00:00:00pages
4149-58issue
6eissn
0006-3495issn
1542-0086pii
S0006-3495(05)73056-3journal_volume
89pub_type
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