This puzzle starts with the sidechains facing away from you.
The first step is to click and drag on the white background to rotate the protein so you can see and grab the sidechains.
Once you can see the sidechains, drag the sidechains on each end away from each other to clear the clashes and solve the puzzle.
Technical stuff: this puzzle has five segments. The sidechains are all hydrophilic. The big sidechain on the left is lysine, and the big sidechain on the right is arginine. The sidechain in the middle is threonine. Threonine has the same shape as valine, but valine is hydrophobic, so it would be orange. In between the segments with sidechains, there are two segments of glycine.