Z. Bian et S. Normark, NUCLEATOR FUNCTION OF CSGB FOR THE ASSEMBLY OF ADHESIVE SURFACE ORGANELLES IN ESCHERICHIA-COLI, EMBO journal, 16(19), 1997, pp. 5827-5836
Curli are surface organelles in Escherichia coli that assemble outside
the bacterium through the precipitation of secreted soluble CsgA mono
mers, requiring the CsgB nucleator protein, Using immunoelectron micro
scopy and immunoblotting assays, CsgB is shown to be located on the ba
cterial surface and also as a minor component of wild-type curli, CsgB
lacking its 20 N-terminal residues when fused to maltose-binding prot
ein (MBP) can still trigger polymerization of CsgA monomers in vivo, H
owever, the resulting surface organelles are only formed at one of the
two bacterial poles and are morphologically distinct from wild-type c
urli, These Bfco organelles (CsgB-Free Curli-related Organelles) are h
ighly regular structures reacting with anti-CsgA, but not anti-CsgB an
tibodies, The CsgB of the active MBP-CsgBII fusion is surface exposed
but, unlike the native CsgB in wild-type curli, is not detectable in t
he Bfco organelles. Overexpression of csgB within a csgA mutant result
s in the formation of short CsgB polymers on the cell surface, It is s
uggested that in wild-type bacteria, both CsgA and CsgB are secreted p
roteins. Interaction between CsgA and CsgB triggers wild-type curli fo
rmation, resulting in CsgA-CsgB heteropolymers, while surface-anchored
CsgB in MBP-CsgBII triggers morphologically distinct, CsgB-free/CsgA
Bfco organelles. In the absence of CsgA, CsgB can self-assemble into p
olymers.