Structural Characterization of Membranes

Additionally it is also possible to study the interaction between proteins and lipids and this is very important for the structural characterization of membrane proteins (Huster 2005). Last but not least, high resolution P NMR is an established method for the determination of the PL composition of complex mixtures (Schiller and Arnold 2002) that can be very easily quantified by using the integral intensities of the individual resonances. Both aspects of P NMR were recently reviewed (Schiller et al. 2007a). 

Over the past 30 years, rapid progress has been made applying supramolecular principles to biomembrane research, and this chapter has endeavored to provide a flavor of key developments in the area. Yet much is left to discover. Many cellular processes occurring in phospholipid bilayers are currently poorly understood, but are yielding to better analytical techniques and improved structural characterization of membrane proteins. These advances will doubtlessly uncover previously unsuspected modes of biomembrane behavior, where stripped-down bionfimetic systems will be... 

Several articles or communications show the use of tomography for the structural characterization of membranes. Thus, studies were published relating to the mechanisms of membrane formation, the experimental acquisition of data such as porosity or tortuosity, the obtaining of realistic 3D models for the simulation of the flows in the membranes, or the detection of defects. 

Hantke K, Nicholson G. Rabsch W, Winkelmann G (2003) Salmochelins, Siderophores of Salmonella enterica and Uropathogenic Escherichia coli Strains, are Recognized by the Outer Membrane Receptor Iron. Proc Natl Acad Sci USA 100 3677 Harada K, Tomita K, Fuji K, Masuda K, Mikami Y, Yazawa K, Komaki H (2004) Isolation and Structural Characterization of Siderophores, Madurastatins, Produced by a Pathogenic Actinomadura madurae. J Antibiot 57 125... 

Farrar, G. H. and Harrison, R. 1978. Isolation and structural characterization of alkali-labile oligosaccharides from bovine milk-fat-globule membrane. Biochem. J. 171, 549-557. 

The two phenomena are furthermore not very suitable for the characterization of membranes, because structural changes may easily occur due to the high pressures which have to be applied. 

Khoo, K.H., Nieto, A., Morris, H.R. and Dell, A. (1997c) Structural characterization of the N-glycans from Echinococcus granulosus cyst membrane and protoscoleces. Molecular and Biochemical Parasitology 86, 237-248. 

Eckerskom, C. and Lottspeich, F. (1993) Structural characterization of blotting membranes and the influence of membrane parameters for electroblotting and subsequent amino acid sequence analysis of proteins. Electrophoresis 14, 831-838. 

The advent of recombinant DNA technology has led to an increased interest in the structural characterization of proteins by spectroscopic methods. Few spectroscopic techniques can provide the amount of information regarding protein secondary and tertiary structure which can be obtained from circular dichroism (CD) spectroscopy. In this chapter we describe the capabilities of CD spectroscopy to provide details on the globular structure of proteins. In addition, we will provide an overview of quantitative secondary structure estimates via CD spectroscopy and of specialized CD methods for studying proteins in contact with membranes and other biomolecules. Certain aspects of protein CD spectroscopy have been previously reviewed [1-19]. 

Mizukami IF, Vinjamuri SD, Trochelman RD, Todd RF, III. A structural characterization of the Mo3 activation antigen expressed on the plasma membrane of human mononuclear phagocytes. J Immunol 1990 144(5) 1841—1848. 

The isolation of lipids from cells or tissues is not as simple and straightforward as one might desire, but is essentially an important adjunct to characterization of membranes (composition, lipid-to-protein ratio, structure proof, definition, new lipids, etc.). While this is recognized by many investigators in the field, it is difficult for the novice in this area to become aware of some of the potential problems in extraction procedures and the reasons for particular approaches. Thus it seems fitting at this point in time to comment on some of the nuances of the approaches used in isolation, purification, and identification of lipids present in cell membranes. These topics are subdivided into areas which are considered to be of major import to a successful consideration of the extraction procedure. 

Phospholipids are hydrophobic molecules present in all living organisms. They are applied as building blocks of cellular membranes, but serve several other functions as well. The most important classes of phospholipids in eukaryotic cells are the sphingomyelins (SM, Figure 21.4) and glycerophospholipids (GPL, Table 21.2), while phosphoglycolipids are found in prokaryotic cells. Fast-atom bombardment ionization (FAE) first enabled the use of MS and MS-MS for the structural characterization of phospholipids. ESI-MS further facilitated this. ESI-MS characterization of phospholipids was reviewed by Pulfer and Murphy [3]. 

J. O. Previato, C. Jones, L. P. B. Gonsalves, R. Wait, L. R. Travassos, A. J. Parodi, and L. Vlendonga-Previato, Structural characterization of the major glycosylphosphatidylinositol membrane-anchored glycoprotein from epimastigote forms of Trypanosoma cruzi Y-strain, J. Biol. Chem., 270 (1995) 7241-7250. 

W. L. Roberts, S. Santikam, V. N. Reinhold, and T. L. Rosenberry, Structural characterization of the glycoinositol phospholipid membrane anchor of human erythrocyte acetylcholinesterase by fast atom bombardment mass spectrometry,./. Biol. Chem., 263 (1988) 18776—18784. 

In many cases, the function of a membrane protein and the topology of its polypeptide chain in the membrane can be predicted on the basis of its homology with another, well-characterized protein. In this section, we examine the characteristic structural features of membrane proteins and some of their basic functions. More complete characterization of the structure and function of various types of membrane proteins is presented in several later chapters the synthesis and processing of this large, diverse group of proteins are discussed in Chapters 16 and 17. 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubility by converting silk I to silk II in a process found useful for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to facilitate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to facilitate structural characterization of the protein (30). Resolubilized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

The TER-XSW method opens the possibility of using XSW to profile nanoscale metal structures and ion distributions above solid surfaces and at fluid-solid interfaces. Applications of TER-XSW have included direct observation of the diffuse electrical double layer at the charged membrane and electrolyte interfaces (Bedzyk et al. 1990 Wang et al. 2001), structural characterization of self-assembled organic monolayers (Lin et al. 1997), and determining metal ion partitioning at oxide-biofilm interfaces (Templeton et al. 2001). These applications are discussed later in this chapter. 

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