Panel A shows the results of an analytic size-exclusion chromatography (S E C) assay and S D S-P A G E of the purified B B K complex, with a peak at 10.39 milliliters. The S E C-M A L S analysis in Panel A indicates a molecular weight of 141 kilodaltons for the B B K complex. Panel B presents the radius of gyration (R g) and scattering intensity (I(0)) versus the number of diffraction frames from an S E C-S A X S experiment measuring the B B K. Panel C displays the pair distribution function P(R) of the B B K. Panel D provides a S A X S-based structural outline of the B B K complex. Panel E shows a S A X S model of the A B K complex with the identifier S A S D M V 5. The K I F 3 B, B, and K A P 3 (B B K) and K I F 3 A, B, and K A P 3 (A B K) complexes share a similar core, the B B K complex exhibits a more compact tail-K A P 3 orientation compared to the A B K model (S A S D M V 5). Panel F illustrates the superposition of the tail-K A P 3 region of the B B K with the A B K, excluding the elongated coiled-coil segment. The graphs and diagrams collectively highlight the biochemical and structural bases underlying the cargo-binding ability and specificity of the K I F 3, B, and K A P 3 complex. All data is approximate.
KIF3B/B/KAP3 has a unique C-terminal structure underlying its cargo specificity. (A) Reconstruction and biochemical evaluation of KIF3/KAP3 BBK complex. Analytic SEC assay and SDS-PAGE result of purified BBK (KIF3-BCT/BCT/KAP3) complex (left panel); SEC-MALS analysis of the BBK complex (right panel). The MW of the complex was found to be 141 kDa, which is close to the theoretical calculation with a 2:1 binding ratio. (B) Rg and I(0) versus number of diffraction frames from SEC-SAXS experiment measuring the BBK. (C) Pair distribution function P(r) of the BBK. (D) SAXS-based structural outline of BBK. (E) SAXS model of ABK (SASBDB ID: SASDMV5). (F) Superposition of the tail-KAP3 region (excluding the elongated coiled-coil segment) of BBK with ABK. (G) Model depicting specific cargo transport by various KIF3/KAP3 subtypes for distinct functions. Source data are available for this figure: SourceData F5.