. Author manuscript; available in PMC: 2018 Oct 1.
Published in final edited form as: J Mol Biol. 2018 Jun 7;430(17):2688–2694. doi: 10.1016/j.jmb.2018.06.008
This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).