A MAJOR OUTER-MEMBRANE PROTEIN OF RAHNELLA-AQUATILIS FUNCTIONS AS A PORIN AND ROOT ADHESIN

A 38-kDa major outer membrane protein (OMP) was isolated from the nitr ogen-fixing enterobacterium Rahnella aquatilis CF3. This protein exist s as a stable trimer in the presence of 2% sodium dodecyl sulfate at t emperatures below 60 degrees C. Single channel experiments showed that this major OMP of R. aquatilis CF3 is able to form pores in the plana r lipid membrane, Two oligonucleotides encoding the N-terminal portion of the 38-kDa OMP and C-terminal portion of OmpC were used to amplify the 38-kDa gene by PCR, The deduced amino acid sequence showed a stro ng homology with Escherichia coli, Klebsiella pneumoniae, Salmonella t yphi, and Serratia marcescens OmpC sequences, except loops L6 and L7, which are postulated to be cell surface exposed, On the basis of the O mpF-PhoE three-dimensional structure, it seems likely that this 38-kDa organizes three 16-strand beta-barrel subunits, The relationship betw een the structure and the double functionality of this protein as pori n and as a root adhesin is discussed.