HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Puntervoll, P. Articles by Jensen, H. B. Search for Related Content PubMed PubMed Citation Articles by Puntervoll, P. Articles by Jensen, H. B. Agricola Articles by Puntervoll, P. Articles by Jensen, H. B.

The Fusobacterium nucleatum porin FomA possesses the general topology of the non-specific porins

Pl Puntervoll¹

Department of Molecular Biology, University of Bergen, HiB, Thormøhlensgate 55, N-5020 Bergen, Norway¹
Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands²

Author for correspondence: Pl Puntervoll. Tel: +47 55584500. Fax: +47 55589683. e-mail: pal.puntervoll{at}mbi.uib.no

FomA is a major non-specific porin of Fusobacterium nucleatum with no sequence similarity to other known porins. According to the topology model, the protein consists of 16 transmembrane ß-strands, connected by eight surface-exposed loops and seven periplasmic turns. In this study, the insertion mutagenesis approach was applied to probe the topology model. A Semliki Forest Virus (SFV) epitope was successfully inserted at 11 different sites of the FomA protein and a 6-aa insertion was successfully inserted at two different sites. Correct folding of the mutant proteins and proper incorporation into the outer membrane were assessed by heat modifiability and by an in vivo porin activity assay. Immunofluorescence microscopy analysis of intact cells, using mAbs directed against the inserted SFV epitope, revealed that three of the eight putative extracellular loops are indeed surface-exposed. Trypsin accessibility experiments confirmed the cell surface exposure of two additional loops. The results support the proposed topology model, showing that FomA possesses the general ß-barrel topology of the non-specific porins, with the interesting exception that the third loop does not seem to fulfil the role of a constriction loop.

Keywords: outer-membrane proteins, porins, Fusobacterium nucleatum, topology, epitope insertion mutagenesis

Abbreviations: wtFomA, wild-type FomA; mFomA, mutant FomA; OMP, outer-membrane protein; SFV, Semliki Forest Virus

This article has been cited by other articles:

				H. Nikaido Molecular Basis of Bacterial Outer Membrane Permeability Revisited Microbiol. Mol. Biol. Rev., December 1, 2003; 67(4): 593 - 656. [Abstract] [Full Text] [PDF]

				P. Puntervoll, M. Ruud, L. J. Bruseth, H. Kleivdal, B. T. Hogh, R. Benz, and H. B. Jensen Structural characterization of the fusobacterial non-specific porin FomA suggests a 14-stranded topology, unlike the classical porins Microbiology, November 1, 2002; 148(11): 3395 - 3403. [Abstract] [Full Text] [PDF]

				H. Kleivdal, P. Puntervoll, and H. B. Jensen Topological investigations of the FomA porin from Fusobacterium nucleatum and identification of the constriction loop L6 Microbiology, April 1, 2001; 147(4): 1059 - 1067. [Abstract] [Full Text]