Chloroplasts assemble the major subunit FaeG of Escherichia coli F4 (K88) fimbriae to strand-swapped dimers.

Inge Van Molle, Jussi Joensuu, Lieven Buts, Santosh Panjikar, Mirkka Kotiaho, Julie Bouckaert, Lode Wyns, Viola Niklander-Teeri, Henri De Greve

Research output: Contribution to journalArticle

25 Citations (Scopus)


F4 fimbriae encoded by the fae operon are the major colonization factors
associated with porcine neonatal and postweaning diarrhoea caused by
enterotoxigenic Escherichia coli (ETEC). Via the chaperone/usher pathway,
the F4 fimbriae are assembled as long polymers of the major subunit FaeG,
which also possesses the adhesive properties of the fimbriae. Intrinsically,
the incomplete fold of fimbrial subunits renders them unstable and
susceptible to aggregation and/or proteolytic degradation in the absence
of a specific periplasmic chaperone. In order to test the possibility of
producing FaeG in plants, FaeG expression was studied in transgenic
tobacco plants. FaeG was directed to different subcellular compartments by
specific targeting signals. Targeting of FaeG to the chloroplast results in
much higher yields than FaeG targeting to the endoplasmic reticulum or the
apoplast. Two chloroplast-targeted FaeG variants were purified from
tobacco plants and crystallized. The crystal structures show that chloroplasts
circumvent the absence of the fimbrial assembly machinery by assembling
FaeG into strand-swapped dimers. Furthermore, the structures reveal how
FaeG combines the structural requirements of a major fimbrial subunit
with its adhesive role by grafting an additional domain on its Ig-like core.
Original languageEnglish
Pages (from-to)791-799
Number of pages9
JournalJ. Mol. Biol.
Publication statusPublished - 2007


  • F4 fimbriae; chloroplast-targeting;
  • chaperone/usher pathway;
  • strand-swapping;
  • enterotoxigenic Escherichia coli

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