Characterization of the Neisseria Iga beta-core. The essential unit for outer membrane targeting and extracellular protein secretion.

Authors:
T Klauser, J Krämer, K Otzelberger, J Pohlner, TF Meyer
Year of publication:
1993
Volume:
234
Issue:
3
Issn:
0022-2836
Journal title abbreviated:
J. Mol. Biol.
Journal title long:
Journal of molecular biology
Impact factor:
6.151
Abstract:
Extracellular transport of Neisseria IgA proteases across the bacterial outer membrane is accomplished by the translocation function contained within the C-terminal Iga beta domain of IgA protease precursor proteins. Recently, we reported that Iga beta from N. gonorrhoeae MS11 (Val1097 to Phe1505), fused to a periplasmic passenger protein, facilitated its transport across the outer membrane, leading to surface exposure of the passenger. In the present work we show, by systematic N-terminal truncation of Iga beta, that the functional and structural unit, termed Iga beta-core, corresponds to the C-terminal approximately 274 amino acid residues (Ser1231 to Phe1505). This minimal region retains all the essential features necessary for the translocation of an N-terminally attached passenger across the outer membrane of Escherichia coli, and for its own correct integration into the outer membrane, even in the absence of a passenger protein. The membrane-integrated Iga beta-core constitutes a conserved entity found in the C-terminal regions of Iga beta domains of different N. gonorrhoeae, N. meningitidis and Haemophilus influenzae strains. In contrast, the surface-exposed N termini of the Iga beta domains vary in size and sequence. Based on secondary structure predictions, the key structural feature of the core is a beta-barrel (amphipathic, antiparallel transmembrane beta-strands, interspersed by hairpin turns and loops) which is common to many integral outer membrane proteins of Gram-negative bacteria. We propose that the core has been conserved in evolution, to provide a selective outer membrane export channel for covalently attached polypeptides.