Protein dynamics in minimyoglobin: is the central core of myoglobin the conformational domain?

Abstract

The kinetics of CO binding to the horse myoglobin fragment Mb-(32-139), the so-called "mini-Mb," were investigated by laser flash photolysis in 0.1 M phosphate buffer and in buffer with 75% (vol/vol) glycerol. The reaction displays complex time courses that can be approximated satisfactorily only with a sum of five exponentials. The features of the kinetic components and a comparison of the deoxy-minuscarbonyl difference spectra of mini-Mb and horse Mb obtained under equilibrium conditions, with the kinetic difference spectra resulting from the global analysis of the traces recorded between 400 and 450 nm, show that CO binding to mini-Mb is accompanied by large structural changes. In view of the fact that mini-Mb is an approximation ofthe Mb-(31-105) fragment encoded by the central exon of the Mb gene, this finding is particularly relevant. On the basis of our data and previous reports

Structure-dynamics-function relationships in Asian elephant (Elephas maximus) myoglobin. An optical spectroscopy and flash photolysis study on functionally important motions

“…10). Very low peak activation enthalpies for CO rebinding have been reported for free heme (Alberding et al, 1976) and for cases in which photolysis dissociates both axial ligands of the iron (Huang et al, 1991;Di Iorio et al, 1993). However, two independent lines of evidence exclude the possibility that process I can be attributed to the photodissociation of the bond with the proximal histidine.…”

Multiple strategies for O2 transport: from simplicity to complexity

“…The lack of the A helix and part of the B and H helices and of some crucial tertiary interactions in mini-Mb represents an important test and a challenge for the folding pathway of apo-Mb proposed by various authors (21,22), who postulated a crucial nucleation role played by the A, G, and H helices. Therefore, the structural stability of mini-Mb (where a key role seems to be played by hydrophobic interactions; see 19) indicates that it may represent a valuable model as a folding intermediate of Mb under non-denaturing conditions, suggesting an alternative sequence of events in the acquisition of native folding in mini-Mb which may or may not be shared under some conditions also by Mb (20).…”