5VGU:
reference: Heterohexamers Formed by CcmK3 and CcmK4 Increase the Complexity of Beta Carboxysome Shells., Sommer M, Sutter M, Gupta S, Kirst H, Turmo A, Lechno-Yossef S, Burton RL, Saechao C, Sloan NB, Cheng X, Chan LG, Petzold CJ, Fuentes-Cabrera M, Ralston CY, Kerfeld CA, Plant Physiol. 2019 Jan;179(1):156-167. doi: 10.1104/pp.18.01190. Epub 2018 Nov, 2. PMID: 30389783

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