THE STRUCTURE OF OMPF PORIN IN A TETRAGONAL CRYSTAL FORM

Background: OmpF porin is a trimeric integral membrane protein respons ible for the passive transport of small hydrophilic molecules, such as nutrients and waste products, across the outer membrane of Escherichi a coli. Very few membrane proteins have been crystallized in three dim ensions, yet this stable protein can be obtained in several crystal fo rms. Comparison of the structures of the same membrane protein in two different packing environments is of major interest, because it allows us to explore the integrity of the structure outside the natural memb rane environment. Results: The structure of OmpF porin in a tetragonal crystal form with two trimers per asymmetric unit has been determined at 3.2 Angstrom resolution and compared with that obtained previously in a trigonal crystal form. The lattice contacts involve only polar a toms, whereas extensive hydrophobic protein-protein interactions were found in the trigonal lattice. The trimer structure is virtually ident ical in both. Conclusions: Our comparison reveals that the overall str ucture of OmpF is not influenced by crystal lattice constraints and, t hus, presumably bears close resemblance to the in vivo structure. The tetragonal crystal structure has provided the starting model for the p hasing of neutron diffraction data obtained from this crystal form, as described in an accompanying article.