CRYSTALLIZATION OF MEMBRANE PROTEINS WITH THE HELP OF ANTIBODY FRAGMENTS. Christian Ostermeier, So Iwata, Hartmut Michel, Max-Planck-Institut fuer Biophysik, Heinrich-Hoffmann-Str.7, 60528 Frankfurt, Germany

For X-ray structure determination of proteins, well-diffracting three-dimensional crystals are required. However, crystallization of membrane proteins remains difficult. Known crystal packing structures indicate that exclusively the polar surfaces of the membrane proteins are responsible for establishing the ordered three-dimensional crystal lattice. Therefore it should be possible to increase the chances for growing well-ordered crystals of a membrane protein through the enlargement of its polar surfaces. Here, we show that the crystallization of the multisubunit membrane protein cytochrome c oxidase from Paracoccus denitrificans became possible due to the complexation with an antibody Fv fragment. The structure was solved to a resolution of 2.8Å. This reveals the secret ot the structure of this redox-driven proton pump, which plays an essential role in the respiratory chain of many organisms. The approach of co-crystallizing membrane proteins with antibody fragments should be useful in obtaining well-ordered crystals of membrane proteins in general.

Ref.: Nature Structural Biology 2, 842 (1995) Nature 376, 660 (1995)