Opening image: Backbone trace of the B and E helices in myoglobin. The close approach of the two helices is possible because two invariant glycine residues (B6 and E8) are present at the crossing. Any side chain larger than a hydrogen atom pushes the helices apart, thereby disrupting the tertiary structure.

Hide the rest of the protein.

Toggle spacefilling of Gly residues. The α carbons are shown in green.

Toggle spacefilling of the E helix. Use the "CORN" mnemonic to imagine where the methyl group would be if GLY B6 (cyan helix) were replaced with alanine.

Toggle highlighting of the side chain of the glycines. The R group (a single hydrogen) is shown in magenta.

The heme is now shown along with the B and E helices. Toggle the following buttons to reveal the two invariant residues on the distal side of the heme: His E7 and Val E11.

Now let's examine the B helix. Leu B10 and Phe B14 are highly conserved in myoglobin and hemoglobin A and B chains. Leu B13 also forms non-covalent interactions with the heme.

We will explore binding of oxygen in the next section.