A proteomic view of probiotic Lactobacillus rhamnosus GG

Review of the Literature
fi ed and separated from the proteins that were
present in the cell before the addition of the
radioactive compound. Another excellent
and relatively recently developed method for
quantitative comparison of proteome populations
is two-dimensional diff erence gel electrophoresis
(2-D DIGE) (Ünlü et al., 1997).
In 2-D DIGE, proteins are labeled using three
diff erent fl uorescent dyes, Cy2, Cy3, and Cy5,
each of which have separate adsorption and
emission characteristics. Using these dyes,
two diff erent protein samples can be quantitatively
compared on a single gel. In addition,
an internal standard can be used to improve
the accuracy of the quantifi cation. Th e three
proteome 2-D images are then scanned from
the gel using three diff erent wavelengths. By
this kind of multiplexing, the eff ect of intrinsic
gel-to-gel variability of the 2-D method can be
diminished.
In addition to gel electrophoretic methods,
bacterial proteomes can be analyzed
using non-gel-based methods. Using highperformance
liquid chromatography and
mass spectrometric methods, it is possible to
separate and identify complex peptide mixtures.
Accurate protein quantifi cation can be
achieved using, e.g., the isotopic labeling of
proteins and peptides (Monteoliva & Albar
2004). Non-gel-based proteomic methods are
useful in high throughput applications and
in the cases where the target is to identify a
maximal number of different proteins. The
gel-based methods, alternatively, are useful,
e.g., in getting an overview of proteome level
changes or when the presence of diff erent
protein isoforms, post-translational modifi cations,
or protein fragments is explored.
6
1.3. Proteomics of poten� al
probio� c bacteria
Proteomics research of probiotic bacteria is
a relatively recent fi eld of research, but proteomics
methods have begun to be exploited
in several studies of probiotics in the last
decade. First, proteomics has been used to
obtain a proteome map or an overview of bacterial
protein content. Second, adaptation to
gut conditions such as low pH and bile acids
has been an important research theme. Proteins
localized on the cell surface have also
been a subject of interest because the cell
surface is the main contact point between
the probiotic and the host. In addition, proteomics
has been used as a tool to answer
various special questions about the molecular
biology of potentially probiotic bacteria. Previous
reviews have discussed the proteomics
of lactic acid bacteria and bifidobacteria in
general (Champomier-Vergès et al., 2002;
De Angelis & Gobbetti, 2004; Di Cagno et
al., 2011; Gagnaire et al., 2009; Manso et al.,
2005; Pessione et al., 2010; Sánchez et al.,
2008c), but only one restricted review focusing
on proteomics of probiotic bacteria (Aires
& Butel, 2011) and two studies about secreted
proteins of probiotics (Sánchez et al., 2008a;
Sánchez et al., 2010b) are available.
In the following chapters, proteome studies
of bacterial strains that are commercially
used or scientifically proven probiotics or
potential probiotics are reviewed. Th ese studies
are also listed in Table 1.