Human Leptin Structure

This is human Leptin.
Spin leptin around and get an overview.

This first glance does not tell you much so let's change its appearance Alpha helices are the red spirals and the white portion lacks secondary structure.

Is this protein composed of a single polypeptide? You know that it is encoded by a single gene. What must have happened to leptin since it was first translated?

How can this one helix stay attached to the others? If you knew that there were two cysteines (yellow) in leptin, would that explain its tertiary structure?

Since the disulfide bond did not link the lone alpha helix to the rest of the protein, there must be some other force keeping them together.

Let's look at the hydrophobic amino acid side chains (dark green) between the lone alpha helix and the rest of the protein.

It appears that these two portions are held together by hydrophobic interactions.

Let's take a closer look at the amino acids that stick out from the core structure. To simplify the view, we will look at the polypeptide backbone with no side chains first.

Tyrosines (dark blue) with hydrophobic benzene ring and protruding -OH group.

Phenylalanines (dark blue) hydrophobic benzene ring.

Glutamic acids (dark red) with a negative charge.

Aspartic acids (dark red) with a negative charge.

Arginines (light blue) with a positive charge.

Lysines ((light blue) with a positive charge.

Histidines ((light purple) with a positive charge.

Do you think these side chains play a critical role in way leptin binds to its receptor? What type of experimentation could you do to test your prediction?

3D Structure of Human Leptin