6SIH:
reference: The cryo-EM structure of the bacterial flagellum cap complex suggests a molecular mechanism for filament elongation., Al-Otaibi NS, Taylor AJ, Farrell DP, Tzokov SB, DiMaio F, Kelly DJ, Bergeron JRC, Nat Commun. 2020 Jun 25;11(1):3210. doi: 10.1038/s41467-020-16981-4. PMID: 32587243

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