G Protein Structure/Function

This molecule was visualized by
Mark A. Wall et al., 1995.
Cell Vol. 83. 1047-1058.

α Chain β Chain γ Chain

GTP in CPK colors C O N P

Familiarize yourself with the structure of a G protein. It is composed of 3 subunits (yellow, purple and red) and is shown here bound with GDP (in CPK colors).

Flip it along the X axis:
Now along the Y axis:

Total Protein Structure

Look at Secondary Structure:

In chime, an alpha helix is shown
as a magenta spiral, like this:

and a beta pleated sheet is a series of yellow ribbons as shown below within the context of some alpha heleces:
sheet hint

Focus on the circularized sevenfold propellar shape.
Rotate around the X axis:
Rotate around the Y axis:

Look at the propellar more closely.
.
Now look at the entire complex again.

Spin on X axis.
Spin on Y axis.

What secondary structure is needed to produce this shape?
Click here for the answer.

GTP/GDP Binding Site

GTP in CPK colors C O N P

GDP is in the Binding Site

Zoom in to see GDP.

Turn Off Slab Mode

Note the two phosphates

Look at the Quaternary Structure.

Given the quaternary structure shown, why does it make sense that GDP is bound instead of GTP?

Click here for the answer.

Let's focus on the amino acids
that bind to GDP . You can click on each colored amino acid to identify it (look in bottom left corner of your browser).

Can you figure out where the third phosphate would be located when GTP is bound to the alpha subunit? Which amino acid(s) would be closest?

G Protein Heterotrimer with GDP Bound

Total Protein Structure

GTP/GDP Binding Site