Myoglobin folding pattern

The first protein structure to be learned was that of myoglobin, which was established by Kendrew et al. in I960.391-393 That of the enzyme lysozyme was deduced by Blake et al. in 1965.394 Since then, new structures have appeared at an accelerating rate so that today we know the detailed architecture of over 6000 different proteins395 with about 300 distinctly different folding patterns 396 New structures are being determined at the rate of about one per day. X-ray diffraction has also been very important to the study of naturally or artifically oriented fibrous proteins397 and provided the first experimental indications of the P structure of proteins. 

Figure 7-23 Folding pattern of the hemoglobin monomers. The pattern shown is for the P chain of human hemoglobin. Some of the differences between this and the a chain and myoglobin are indicated. Evolutionarily conserved residues are indicated by boxes, I I highly conserved, I I invariant. Other markings show substitutions observed in some abnormal human hemoglobins. Conserved residues are numbered according to their location in one of the helices A-H, while mutant hemoglobins are indicated by the position of the substitution in the entire a and P chain.

In the example of Figures 5.14 and 5.15, a knot theoretical polynomial characterization of the folding pattern of myoglobin is given. In Figure 5.14, the... 

The tertiary structure of a protein is the folding pattern of the secondary structural elements into a three-dimensional conformation, as shown for the LDH domain in Figure 7.8. As illustrated with examples below, this three-dimensional structure is designed to serve all aspects of the protein s function. It creates specific and flexible binding sites for ligands (the compound that binds), illustrated with actin and myoglobin. The tertiary structure also maintains residues on the surface appropriate for the protein s cellular location, polar residues for cytosolic proteins, and hydrophobic residues for transmembrane proteins (illustrated with the P2-adrenergic receptor). 

Proteins are folded in many ways. We have already considered several simple patterns the antiparallel P cylinder (Fig. 2-16), the 2-helix coiled coil (Fig. 2-21) and the 3- and 4-helix bundles (Fig. 2-22). Another simple motif that has been found repeatedly is the helix-turn -helix or helix-loop-helix in which two helices at variable angles, one to another and with a turn or short loop between them, form a structural emit. DNA-binding repressors and transcription factors (see Fig. 2-21 and also Chapter 5) often contain this motif as do many Ca2+-binding proteins. Proteins containing 3-6 helical segments, often fold into a roughly polyhedral shape.258 259 An example is myoglobin (Fig. 2-19B). 

It is believed that myoglobin and haemoglobin are derived from a common ancestral gene and that the pattern of folding of the globin chain represents Nature s basic design for 02-carrying proteins (see the next section). 

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