4ZQU:
reference: Diversification of beta-Augmentation Interactions between CDI Toxin/Immunity Proteins., Morse RP, Willett JL, Johnson PM, Zheng J, Credali A, Iniguez A, Nowick JS, Hayes CS, Goulding CW, J Mol Biol. 2015 Nov 20;427(23):3766-84. doi: 10.1016/j.jmb.2015.09.020. Epub, 2015 Oct 9. PMID: 26449640

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