DETERGENT BINDING IN TRIGONAL CRYSTALS OF OMPF PORIN FROM ESCHERICHIA-COLI

The structure of the detergent, ocytyl hydroxyethylsufoxide (C8(HE)SO) , bound to the OmpF porin from E coli (in the trigonal crystal form) h as been determined by neutron crystallography. Due to a dynamic exchan ge of detergent molecules with their environment they are not ordered on an atomic scale. The structure reported here is therefore at a reso lution of similar to 16 Angstrom. The X-ray crystallographically deter mined structure of the protein provides a starting point for the neutr on analysis in which the detergent is visualised primarily thanks to i ts high contrast against D2O. The structure shows the detergent to be located mainly in two areas. It forms toroidal annuli around each OmpF trimer, these annuli fusing to form a detergent belt surrounding a so lvent filled column traversing the crystal. Those areas of the protein to which the detergent binds are formed almost exclusively of hydroph obic residues and form a band about 30 Angstrom high around the trimer . Its upper and lower bounds are defined by two bands of aromatic resi dues, tyrosines pointing away from the detergent belt and interacting with the polar headgroups while phenylalanines point inwards. This str ongly suggests that the same areas define, in vivo, the location at wh ich protein interacts with lipid. The hydrophobic moiety of detergent is also found mediating the hydrophobic protein-protein interactions a t the interface between two trimers on the crystallographic two-fold a xis ((C) Societe francaise de biochimie et biologie moleculaire / Else vier, Paris).