Fig. 9: Flexible linker distances and a comprehensive model for the organization of the OGDHc.

A Graph representing the mean distance values of the binned groups of all unresolved amino-acid sequences belonging to all protein structures deposited in the PDB. Black dots represent the mean value of a length of amino-acids group, with varying scales of gray the standard deviation after the integration of each quartile of total data, as denoted in the plot legend. The red line represents a fitted model that describes the relationship between the distance and the length of amino-acid groups. With light green the experimentally measured average distance between the N-ter of the resolved core domain of the E2o and the C-ter of the LD that is bound to a fitted E1o dimer on the periphery, while dark green represents the same average distance experimentally measured between the N-ter of the resolved core domain of the E2o and the C-ter of the LD that is bound to a fitted E3 dimer. The blue line represents the theoretical distance of an amino-acid sequence, while the dashed blue line represents the theoretical lower limit of any amino-acid sequence. B Schematic representation of the peripheral subunit organization of the resolved OGDHc. C Model describing all the novel observations concerning the organization of the OGDHc. The N-ter β-sheet conformation of the E2o core vertex trimer helps stabilize and compact the 24-mer E2o core, while simultaneously orienting the flexible linker that connects the LD domain. Cross-linking data reveals a fairly stable interaction between the flexible linker and the peripheral subunits, possibly hinting at a structural role of an un-loaded LD domain, while another, loaded LD domain performs the reaction cycling. The interaction between the LD and the peripheral subunits is governed by strong electrostatic forces.