The idea is to drag the ends of the protein toward each other. This puzzle can be a little tricky compared to the earlier ones. If you drag the ends too close together, you'll see the voids turn into clashes. Using the shake tool may help clear the clashes, but you may need to reset and try again a few times. You don't need to totally eliminate the voids, but they should be much smaller. Using shake at the end may help finish the puzzle. The two curly helixes should be parallel to each other when you're done.