The evolutionarily related beta-barrel polypeptide transporters from Pisum sativum and Nostoc PCC7120 contain two distinct functional domains.
Several beta-barrel-type channels are involved in the translocation or assembly of outer membrane proteins of bacteria or endosymbiotically derived organelles. Here we analyzed the functional units of the beta-barrel polypeptide transporter Toc75 (translocon in outer envelope of chloroplasts) of the outer envelope of chloroplasts and of a protein, alr2269, from Nostoc PCC7120 with homology to Toc75, both proteins having a similar domain organization. We demonstrated that the N-terminal region functions as a recognition and complex assembly unit, whereas the C terminus forms the beta-barrel-type pore. The pore region is, in turn, modulated by the N terminus of the proteins. The protein from Nostoc PCC7120, which shares a common ancestor with Toc75, is able to recognize precursor proteins destined for chloroplasts. In contrast, the recognition of peripheral translocon subunits by Toc75 is a novel feature acquired through evolution.
Ertel
Franziska
F
Department of Biology I, Ludwig Maximilians University, Menzinger Strasse 67, 80638 München, Germany.
Mirus
Oliver
O
Bredemeier
Rolf
R
Moslavac
Suncana
S
Becker
Thomas
T
Schleiff
Enrico
E
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D017124:Conserved Sequence; D019143:Evolution, Molecular; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046937:Nostoc / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C115176:Omp85 protein, Neisseria; D010940:Plant Proteins