5 research outputs found
Characterization of Heme Orientational Disorder in a Myoglobin Reconstituted with a Trifluoromethyl-Group-Substituted Heme Cofactor
The
orientation of a CF<sub>3</sub>-substituted heme in sperm whale
myoglobin and L29F, H64L, L29F/H64Q, and H64Q variant proteins has
been investigated using <sup>19</sup>F NMR spectroscopy to elucidate
structural factors responsible for the thermodynamic stability of
the heme orientational disorder, i.e., the presence of two heme orientations
differing by a 180° rotation about the 5–15 <i>meso</i> axis, with respect to the protein moiety. Crystal structure of the
met-aquo form of the wild-type myoglobin reconstituted with 13,17-bisÂ(2-carboxylatoethyl)-3,8-diethyl-2,12,18-trimethyl-7-trifluoromethylporphyrinatoironÂ(III),
determined at resolution of 1.25 Ă…, revealed the presence of
the heme orientational disorder. Alterations of the salt bridge between
the heme 13-propionate and Arg45Â(CD3) side chains due to the mutations
resulted in equilibrium constants of the heme orientational disorder
ranging between 0.42 and 1.4. Thus, the heme orientational disorder
is affected by the salt bridge associated with the heme 13-propionate
side chain, confirming the importance of the salt bridge in the heme
binding to the protein