9 research outputs found
Structure and function of protein-lipid systems
Biomembranes play many structural and functional roles in both prokaryotic
and eukaryotic cells [10]. They define compartments, the communication between
the inside and outside of the cell. The main components of biomembranes are
lipids and proteins, which form protein-lipid bilayer systems [10]. A structure and
physicochemical properties of protein-lipid membranes, which determines biological
activities of biomembranes, are strongly dependent on interactions between
lipid and protein components and external agents such as a temperature, pH, and
a membrane hydration [4]. A lipid bilayer matrix serves as a perfect environment
for membrane proteins (Fig. 1), and it assures activities of these proteins. Because
biomembranes are composed of many different groups of lipids and proteins and
have a complex structure, it is difficult to study in details their physicochemical
properties using physicochemical methods. For these reason, lipid membranes of
liposomes are used in many scientific laboratories for studding processes associated
with a lipid phase transition, a membrane hydration, or protein-membrane interactions.
The structure of liposomes (Fig. 5), and an influence of pH and an ionic
strength on a lipid bilayer structure are discussed in the presented work. The role
of membrane proteins in determination of biological activities of biomembranes is
highlighted. A high variety of a structure and an enzymatic activity of membrane
proteins is responsible for a high diversity of biological functions of cell membranes
[2]. α-Lactalbumin (α-LA) is a peripheral membrane protein (Figs 8 and 9), its
biological function is strongly related to its conformational structure and interaction
with lipid membranes [49]. The complex of α-LA in a molten globule conformational
state with oleic acid, termed as a HAMLET complex, are disused in a context of
its anti-tumor activity
FTIR-ATR and fluorescence studies of protein-lipid systems
Lipid-protein systems paly curtail roles in living systems [49]. Hence, a determination
of their structure at different levels of organization is still one of the most
important tasks in many research projects. A study of lipid-protein systems is based
on many physicochemical techniques, such as spectroscopy of FTIR, Raman, fluorescence,
NMR, EPR, as well as DLS, DSC and TEM methods. In the presented
paper tow of the most frequently used methods, that is FTIR and fluorescence
spectroscopy, will be discussed in details. They are characterized by a relatively low
cost of sample preparation, a short measuring time, and they give a huge number
of structural and physicochemical information about lipid-protein systems. In the
FTIR-ATR spectroscopy many of vibrational bands are commonly used as very precise
vibrational indicators of structural changes in lipids and proteins (Fig. 1) [1–6].
They allows to characterize lipid and protein components separately in mixed systems.
Additionally, structural changes in lipid membranes can be monitored in one
FTIR-ATR experiment simultaneously in a region of hydrophilic lipid head-groups
(Fig. 5) [17, 18], in a hydrophobic part composed of hydrocarbon lipid chains (see
Figures 2 and 3) [7–9], and in a lipid membrane interface represented by ester lipid
groups (Fig. 4) [4, 6, 11, 12]. A secondary structure of proteins and peptides in different
experimental conditions can be defined in the FTIR-ATR spectroscopy on the
base of amide I bands (Fig. 6 and Tabs 1, 2 and 3) [20–22]. A fluorescence spectroscopy
is a complementary methods to FTIR spectroscopy in a study of lipid-protein
systems. It competes information about time-dependent and very fast (in a scale
of femtoseconds) structural processes in both lipids [41–45] and proteins [23, 27,
48]. The folding, denaturation, and aggregation of proteins and lipid membranes
accompanied by changes in an order, packing and hydration of the system under
study [23, 27, 41–45, 48]