Shown in Figure 7.1 glucagon
Parvalbumin and DNA binding protein previously shown in Figure 5.3 and Figure 5.4 respectively.
Example of this is the engrailed homeodomain DNA binding protein shown in Figure 7.2
This is the most common type of all the alpha subclass. Examples are cytochrome b562, cytochrome c', ferritin, myohemerythin, growth hormone and other cytokines (IL2, IL4, GM-CSF). Also found in ROP dimer previously seen in Figure 5. Figure 7.3 also shows the four helix bundle in myohemerythrin (a marine worm protein with analagous function to haemoglobin).
The four helix bundle can take on different layouts:
Two different orientations - a right orientation (the most common) and a left orientation (Figure 7.4).Up and down connections as shown in Figure 7.4 (80-90% of connections are this type) or crossover connections (Figure 7.5)
Figure 7.6 shows that the four helices in the bundle interact such that the hydrophobic residues are located in the core of the bundle and the hydrophillic residues are located towards the environment
This domain structure is found in a large group of proteins such as: algae, phycocyanins, myoglobin and haemoglobin.
In this class the whole protein is considered the one domain type. The prime example in this class is myoglobin (Figure 1.12) which has eight helices, but does not really have any defined arrangement of smaller structural motifs (although there is one helix-turn-helix between helix G and helix H).
The globins are a good example of proteins which can have vastly different amino acid primary sequences, but still develop a similar 3-D structure.