Deoxymyoglobin studied by the conformational normal mode analysis. I. Dynamics of globin and the heme-globin interaction

Dynamic properties of deoxymyoglobin are studied theoretically by the analysis of conformational fluctuations. Root-mean-square atomic fluctuations and distance fluctuations between different segments reveal the mechanical construction of the molecule. Eight alpha-helices behave as relatively rigid bodies and corner regions are more flexible, showing larger fluctuations. More particularly, corner regions EF and GH are specific in that flanking alpha-helices extend their rigidity up to a point in the corner region and the two rigid segments are connected flexibly at that point. The FG corner is exceptional. A segment from the F helix to the beginning of the G helix, in which the FG corner is included, becomes relatively rigid by means of strong interactions with the heme group. The whole myoglobin molecule is divided into two large units of motion, one extending from the B to the E helix, and the other from the F to the H helix. These two units are connected covalently by the EF corner. However, dynamic interactions between these two units take place mainly through contacts between helices B and G and not through the EF corner. From correlation coefficients between fluctuational motions of residues and the heme group, 55 residues are identified as having strong dynamic interactions with the heme moiety. Among them, 18 residues in the three segments, one consisting of residues from the C helix to the CD corner, a second consisting of the E helix, and a third from the F helix to the beginning of the G helix, are in close contact with the heme group. Twenty-two of the 55 residues are within four residues of the 18 residues in their sequential residue number and are more than 3 A away from the heme group. The other 15 residues are located further in the sequential residue number and are all found in helices A and H. They are more than 6 A away from the heme group. By the use of correlation coefficients of fluctuations between residues, it is found that dynamic interaction with the heme group is transmitted to the A helix and the beginning of the H helix in the direction Leu(E15)----[Val(All) and Trp(A12)]. The transmission to the C-terminal end of the H helix is mediated by a long segment, from the end of the EF corner to the beginning of the G helix, that lies on the heme group and has close contacts over a wide range.(ABSTRACT TRUNCATED AT 400 WORDS)