The protein in question, a retroviral protease, had been known for 15 years. It had been solved by NMR (nuclear magnetic resonance) in 2003, but the NMR results were inconsistent with results from X-ray crystallography. Puzzle 390 launched 17 December 2010, and completed 7 January 2011. Using 10 starting models taken from NMR results, Foldit players were able to determine the correct native structure of the protein. The puzzle used the alignment tool which allowed players to use partial threading to select portions of different models.