Figure 1. FEZ1 Is a Specific CA Hexamer Sensor.

(A) Schematic diagram of the FEZ1 constructs (marked by the black dotted lines) used for capsid-binding assays. The yellow bar indicates the predicted coiled-coil region of FEZ1. The putative functional regions of FEZ1 are labeled with different colors.

(B) Copelleting assay of FEZ1_1–392, FEZ1_1–92, FEZ1_92–198, and FEZ1_198–392 with 14C/45C crosslinked CA tubes in 150 mM NaCl. Full-length FEZ1_1–392 and FEZ1_92–198 copellet with CA tubes, while the N-terminal (FEZ1_1–92) and C-terminal (FEZ1_198–392) regions do not. T, total load; S, supernatant; P, pellet.

(C–H) Size-exclusion chromatography (SEC)-binding assay of FEZ1_92–198 with different CA assemblies (schematics shown in cartoon insets). The concentrations of FEZ1 and CA monomer in each binding reaction were 33 and 98 μM, respectively. FEZ1_92–198 does not coelute with CA monomer (C), 1/3-hexamer (D), or 1/2-hexamer_EE (E) in SEC assays. There is no elution shift of the mixture (solid purple) relative to the individual components (dotted lines). FEZ1_92–198 does coelute with the CA hexamer (G), and restoration of a hexamer from two 1/2-hexamers (cyan and pink cartoons) restores FEZ1_92–198 coelution (F), which coelutes at the same position as with CA hexamers. In contrast, FEZ1_92–198 does not coelute with hexamer-2_foldon (purple cartoon), which also contains 6 CA subunits but arranged around the 3-fold capsid interface (H).

See also Figure S2.