4YY2:
reference: Rational design of alpha-helical tandem repeat proteins with closed architectures., Doyle L, Hallinan J, Bolduc J, Parmeggiani F, Baker D, Stoddard BL, Bradley P, Nature. 2015 Dec 24;528(7583):585-8. doi: 10.1038/nature16191. Epub 2015 Dec 16. PMID: 26675735

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