4TSM:
reference: Structural and Evolutionary Analyses Show Unique Stabilization Strategies in the Type IV Pili of Clostridium difficile., Piepenbrink KH, Maldarelli GA, Martinez de la Pena CF, Dingle TC, Mulvey GL, Lee A, von Rosenvinge E, Armstrong GD, Donnenberg MS, Sundberg EJ, Structure. 2015 Feb 3;23(2):385-96. doi: 10.1016/j.str.2014.11.018. Epub 2015 Jan, 15. PMID: 25599642

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