Figure 4.

Interactions between CcmK3 and CcmK4 in heterohexamers determined by XFMS. A, Alignment of the sequences of CcmK2, CcmK3, and CcmK4 of Syn7942 and Halothece for reference. Conserved residues involved in interoligomer (lateral tiling) contacts are shaded brown, and those facing the intermonomer interface are yellow. Asterisks indicate substitutions of conserved residues at the interoligomer surface in CcmK3. Numbering below follows Halothece CcmK3. Boxes highlight important regions. B, Ratio of dose response to irradiation of CcmK3 residues, comparing a CcmK3-CcmK4 heterocomplex to isolated CcmK3. C, Concave surface of a CcmK3 model replacing a protomer of a CcmK4 hexamer. Blue coloring shows residues in CcmK3 buried upon interaction with CcmK4 as determined by decreased dose response. D, Structural model of a CcmK3-CcmK4 heterohexamer (assuming 1:2 ratio and symmetrical distribution). Two residues involved in interoligomer contacts in CcmK4 (D50, R81) are colored in green, and the residues replacing them in CcmK3 are in red.