It may be difficult to know the exact function of CSs in cells. Roberts [22]
classified poly-beta-hydroxybutyrate (a PHB) as belonging to CSs. It might act so,
if the concentration of monomers could be regulated enzymically for increasing the
ionic strength and vice versa. However, this and also some other CSs could be used
as energy or phosphorus storages. The most advantageous way for a cell is to exploit
them for dual- or multi-purposes, as osmo- and/or pH-regulators as and energy/
nutrient storage and even maintaining the dynamics of proteins structures. It is
peculiar that CSs tend to occur in cells at high intracellular concentrations. For
getting relevant dynamic data, effective analysis methods are needed. Because of the
high concentrations, nondestructive NMR methods of studying compatible solutes
inside cells in different conditions can be advantageously applied [22]. Bound/solid
and free molecules may be differentiated, while the intracellular pH data could be
simultaneously monitored. The NMR methods for measuring intracellular pH are
based on the chemical shift value of an atom of a known compound near an ionizable
functional group. It is compared with the chemical shift of the same molecule in
solution in different pHs. The chemical shift values should be evaluated critically
because the molecules may not be free inside the cell but bound to other molecules.
The binding can affect the pK a values (and through it to chemical shifts of the
indicator atom). Then the intracellular pH can be misinterpreted. The proton activity
and the whole concept of pH are also strongly dependent on the polarity of the
solvent/microenvironment. For instance, protonation of vitamin B6 bound to its
apoenzyme was misinterpreted in a series of publications because of assuming that
the situation is similar to free vitamin B6 in solution [23]. The same potential source
of errors exists with the usual pH-indicator dyes when measuring internal pH of
a cell.
Numerous CSs are already commercially available, and it is believed that CSs
have a significant commercial potential. However, finding a suitable compound to a
certain application from a long list is not easy. Further fundamental research is
required to find out general guidelines how to use a certain CS. Biological antifreeze
compounds are known for a long time and are likely to share related features with
CSs for the interaction with water molecules. Crystal structures (and NMR studies)
of proteins harboring CSs probably unveil their mechanisms of action and thus
help obtaining reason-based means to test a CS for a specific purpose. After the
basic knowledge is available, molecular modeling studies may be exploited, as
well. Structures of two alkaliphile-produced compatible solutes, ectoine and
hydroxyectoine (Fig. 2), are already known in molecular level for their effects on
protein stability and folding (see [18] and references therein).
Ectoine is commercialized and used as an active ingredient in skin care. It
stabilizes proteins and other cellular structures and protects the skin from stresses
like UV irradiation and dryness. In addition to their uses in research, medicine, and
agriculture sectors, ectoines could also be used for formulating various products with
other CSs.
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E. Khalikova et al.
classified poly-beta-hydroxybutyrate (a PHB) as belonging to CSs. It might act so,
if the concentration of monomers could be regulated enzymically for increasing the
ionic strength and vice versa. However, this and also some other CSs could be used
as energy or phosphorus storages. The most advantageous way for a cell is to exploit
them for dual- or multi-purposes, as osmo- and/or pH-regulators as and energy/
nutrient storage and even maintaining the dynamics of proteins structures. It is
peculiar that CSs tend to occur in cells at high intracellular concentrations. For
getting relevant dynamic data, effective analysis methods are needed. Because of the
high concentrations, nondestructive NMR methods of studying compatible solutes
inside cells in different conditions can be advantageously applied [22]. Bound/solid
and free molecules may be differentiated, while the intracellular pH data could be
simultaneously monitored. The NMR methods for measuring intracellular pH are
based on the chemical shift value of an atom of a known compound near an ionizable
functional group. It is compared with the chemical shift of the same molecule in
solution in different pHs. The chemical shift values should be evaluated critically
because the molecules may not be free inside the cell but bound to other molecules.
The binding can affect the pK a values (and through it to chemical shifts of the
indicator atom). Then the intracellular pH can be misinterpreted. The proton activity
and the whole concept of pH are also strongly dependent on the polarity of the
solvent/microenvironment. For instance, protonation of vitamin B6 bound to its
apoenzyme was misinterpreted in a series of publications because of assuming that
the situation is similar to free vitamin B6 in solution [23]. The same potential source
of errors exists with the usual pH-indicator dyes when measuring internal pH of
a cell.
Numerous CSs are already commercially available, and it is believed that CSs
have a significant commercial potential. However, finding a suitable compound to a
certain application from a long list is not easy. Further fundamental research is
required to find out general guidelines how to use a certain CS. Biological antifreeze
compounds are known for a long time and are likely to share related features with
CSs for the interaction with water molecules. Crystal structures (and NMR studies)
of proteins harboring CSs probably unveil their mechanisms of action and thus
help obtaining reason-based means to test a CS for a specific purpose. After the
basic knowledge is available, molecular modeling studies may be exploited, as
well. Structures of two alkaliphile-produced compatible solutes, ectoine and
hydroxyectoine (Fig. 2), are already known in molecular level for their effects on
protein stability and folding (see [18] and references therein).
Ectoine is commercialized and used as an active ingredient in skin care. It
stabilizes proteins and other cellular structures and protects the skin from stresses
like UV irradiation and dryness. In addition to their uses in research, medicine, and
agriculture sectors, ectoines could also be used for formulating various products with
other CSs.
168
E. Khalikova et al.