Combined use of Crystallography and CryoEM in the structure determination of giant hemocyanins

Hemocyanins are extremely large protein complexes (M_R up to 8.0 MDa) which cooperatively bind oxygen at their type 3 copper active sites. Structural analysis of hemocyanins is a challenge due to their very large size. However, in recent years advances have been made by a combination of cryoEM reconstruction and X-ray crystallography [1-4]. Here we present our recent results such as the 6.5 Å X-ray crystallographic structure of scorpion hemocyanin (1.8 MDa, Fig. 1A), which in connection with its respective cryoEM structures gives a clue for structural changes associated with activation of its intrinsic phenoloxidase activity [1]. Furthermore results on the crystallographic analysis of the native Octopus hemocyanin decamer (3.6 MDa) and the structure of a single functional unit (KLH1-h, Fig. 1B) of Keyhole limpet hemocyanin, which is of medical importance in cancer treatment, will be presented [2-4].

Acknowledgements: Financed by GK 1043 (DFG), the "Computational Science Mainz" (CSM) and "Research Center Immunology" (FZI) of the Gutenberg University. We thank T. Barends & I. Schlichting (MPI Heidelberg) for providing access to X-ray sources, Y. Cong & W. Chiu (NCMI, Houston) for CryoEM reconstructions and G. Schroeder (Forschungszentrum Jülich) for low resolution refinement.

Fig. 1: Hemocyanin