5KF4:
reference: Crystal structure of the second fibronectin type III (FN3) domain from human collagen alpha1 type XX., Zhao J, Ren J, Wang N, Cheng Z, Yang R, Lin G, Guo Y, Cai D, Xie Y, Zhao X, Acta Crystallogr F Struct Biol Commun. 2017 Dec 1;73(Pt 12):695-700. doi:, 10.1107/S2053230X1701648X. Epub 2017 Nov 21. PMID: 29199991

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