Structural detail of the immunoglobulin fold in each domain

Here we see an isolated C_L domain, using cartoon rendering.

Renderings:

trace cartoon planks

Colour:

As we have seen before, each domain has a disulfide bond; note its central location, where it helps hold together the set of two beta sheets and so stabilises the domain tertiary structure.

The third cysteine residue which is not forming the disulfide bond, is the one linking this light chain to the C_H domain in the heavy chain (through one of the 4 interchain links, studied in a previous section).

Let's now cut through the molecule:
Note how the polypeptide chain backbone forms two layers that, in a sort of “sandwich”, enclose the hydrophobic residues of the molecule, while the sidechains in hydrophilic residues stay oriented outwards, exposed to the aqueous environment.

You may shift the slab plane using this slider:

back

front

(it only works after clicking the “prepare” button above)

Recommended orientations:

Quiz:

Locate the disulfide bond (by shifting the slab plane).
Where is it positioned?

How are the two layers of the sandwich generated?

Let's display just the backbone atoms: . Move the model.
Let's cancel the slabbing . Move the model.

The two layers in the sandwich are two beta sheets , which constitute the major part of this domain; let's study them:

rendering
Let's add

Quiz:

How many strands form each sheet?

and