Review for 10.1186/1471-230X-9-58 (2009)

Reviewer's report
Title:The Pancreatic Zymogen Granule Membrane Protein, GP2, Binds
Escherichia coli Type 1 Fimbriae
Version: 1Date:8 April 2009
Reviewer: Luis Angel A Fernández Herrero
Reviewer's report:
General comment and major essential revisions
The manuscript by Yu and Lowe reports that the major pancreatic zymogen
protein GP2 binds to E. coli bacteria expressing type I fimbriae with its tip
adhesin FimH. Type I fimbriae and long proteinaceus filaments expressed by
most E. coli strains, e.g. extraintestinal E. coli strains, and play an essential role
for bacterial adhesion and colonization of host tissues (e.g. human bladder).
FimH binds to glycoproteins containing D-mannosyl residues.
The function of GP2 is not known, but its sequence is 52% identical to
Uromodulin, a protein expressed in the kidney and secreted in the urine that has
been reported to bind to FimH and to play an important role in host defense
against uropathogenic E. coli infections, using animal models. Based on its
similarity to Uromodulin, the authors test whether GP2 binds to bacteria
expressing FimH.
The authors show a specific binding of purified human GP2 to several E. coli
strains expressing type I fimbriae and FimH. No binding is found to several E. coli
mutants lacking type I fimbriae and FimH. Binding is abrogated when GP2 is
deglycosilated in vitro and when D-mannose is added to the incubation reaction,
indicating that the D-mannose binding activity of FimH is associated to the
recognition of GP2. In general the reported experiments have the appropriated
controls and provide sufficient evidence indicating that GP2 binds to bacteria
expressing type I fimbriae and FimH. However, a direct interaction between
purified FimH/FimC complex and GP2 is not demonstrated and the specificity
experiments of GP2 for certain FimH variants are simply based on binding to
bacterial cells, which may express different amounts of type I fimbriae on their
surface. The main conclusion of the paper will be more solid if in vitro
experiments with purified FimH/FimC and GP2 are included to demonstrate a
direct recognition between these proteins. It would be interesting to compare the
binding affinity curves of purified FimH/FimC to GP2 and Uromodulin.
Authors also propose that GP2, similarly to Uromodulin, may have a role in host
defense against E. coli infections. This is the major biological implication of this
paper. However, this hypothesis is not supported by any experiments and,
therefore, the biological significance of the binding of GP2 to bacteria expressing
type I fimbriae remains highly speculative. Given the absence of animal models, I
suggest that this hypothesis should be mentioned only in the Discussion and not
in the Summary (or Title) of this work.
In summary, I believe this manuscript reports an interesting observation
regarding the binding of GP2 to fimbriated bacteria. In addition to the
experiments presented, further in vitro binding experiments with purified
components are needed to demonstrate and measure the affinity of the
interaction between FimH and GP2, and compare it to Uromodulin. Based on the
similarity of GP2 to Uromodulin, authors propose a biological function of GP2 in
host defense against bacterial infections. The proposed function is interesting
and very attractive, and it may justify the publication of this work in BMC
Gastroenterology, although this hypothesis is not demonstrated in the current
manuscript.
Minor essential revisions
- Figure 4 is not referred in the text.
- Authors should change the way the represent the units of "bound bacteria" in
their binding assays. The authors actually measure the radioactivity associated to
the microtiter plate, and not the Colony Forming Units (as is shown in the
Figures) -bound bacteria are not plated and colonies are not counted-. Authors
employ radioactively labelled bacteria and measure the "radioactive counts" after
the binding assay. Thus CFUs should be changed and radioactive units (cpm)
should be indicated.
-The paper is brief but it contains sufficient introduction and references to
previous published work. I found this manuscript easy to read and follow and
Figures follow the standards of presentation.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
'I declare that I have no competing interests'