Date Published: , 2011
Publisher: A.I. Gordeyev
Author(s): K.S. Mineev, E.V. Bocharov, P.E. Volynsky, M.V. Goncharuk, E.N. Tkach, Ya.S. Ermolyuk, A.A. Schulga, V.V. Chupin, I.V. Maslennikov, R.G. Efremov, A.S. Arseniev.
Specific interactions between transmembrane α-helices, to a large extent, determine the biological function of integral membrane proteins upon normal development and in pathological states of an organism. Various membrane-like media, partially those mimicking the conditions of multicomponent biological membranes, are used to study the structural and thermodynamic features that define the character of oligomerization of transmembrane helical segments. The choice of the composition of the membrane-mimicking medium is conducted in an effort to obtain a biologically relevant conformation of the protein complex and a sample that would be stable enough to allow to perform a series of long-term experiments with its use. In the present work, heteronuclear NMR spectroscopy and molecular dynamics simulations were used to demonstrate that the two most widely used media (detergent DPC micelles and lipid DMPC/DHPC bicelles) enable to perform structural studies of the specific interactions between transmembrane α-helices by the example of dimerizing the transmembrane domain of the bitopic protein glycophorin A. However, a number of peculiarities place lipid bicelles closer to natural lipid bilayers in terms of their physical properties.
Membrane proteins constitute more than 25% of the proteome , fulfilling some important functions; they ensure the uniqueness of the biological role of each cell membrane and determine its physicochemical properties. The most important cell processes, such as intercellular reception and communication, molecular and ion transport, membrane fusion, etc., are directly associated with the participation of membrane proteins. Interaction between the transmembrane (TM) domains of proteins that are capable of oligomerizing in the membrane is, in many cases, important for the manifestation of their activity. The so-called bitopic membrane proteins, which have a single TM α-helical segment, play the key role in numerous biological processes taking place in the human organism. The regulation of the activity of bitopic proteins in most cases is associated with homo- or hetero-dimerization in the cell membrane, with the active participation of their TM domains [2, 3]. This class of proteins comprises the majority of receptor protein kinases, immunoreceptors, and apoptosis proteins, which play a direct part in controlling the development and homeostasis of all organism tissues, both in the normal and pathological states.
Preparation of NMR samples of the recombinant GpA 61–98 TM fragment (GpAtm) in membrane-like media
Spatial structure and intramolecular mobility of the GpAtm dimer
A comparative study of the spatial structure and dynamics in two membrane-like media of different types has been carried out for the first time for specifically interacting TM helices. This significant methodological moment allows one to arrive at the conclusion that in the case of the GpA TM domain, the general topology of the dimer, determined by the specific character of the helix-helix interaction, is independent of the selection of the membrane-like medium; only the local structures of TM helices are to a certain extent sensitive to this factor. On the other hand, it is known that the disc-shape and lipid composition of bicelles brings them closer to a natural lipid membrane in terms of physical properties, which results in a decrease in both the conformational fluctuations of helices and the fluctuations of the parameters characterizing their relative arrangement (angle θ and distance d between the helices). In turn, other conditions being equal, this should enhance the stability of the spatial structure of the α-helix membrane protein in bicelles, as compared with that in micelles.