Membrane protein circular

FT-IR spectroscopy is particularly useful for probing the structure of membrane proteins. Until recently, a lack of adequate experimental techniques has been the reason for the poor understanchng of the secondary structure of most membrane proteins. X-ray diffraction requires high quality crystals and these are not available for many membrane proteins. Circular dichroism (CD) has been widely used for studying the conformation of water-soluble proteins, but problems arise in its use for membrane proteins. The light scattering effect may distort CD spectra and lead to substantial errors in their interpretation. In addition, the reference spectra used for the analysis of CD spectra are based on globular proteins in aqueous solution and may not be applicable to membrane proteins in the hydrophobic environment of lipid bilayers. 

Swords, N.A. and Wallace, B.A 1993. Circular dichroism analyses of membrane proteins Examination of environmental effects on bacteriorho-dopsin spectra. Biochem. J. 289 215-219. 

Membrane proteins often contain a-helical sections. We have developed a method called oriented circular dichroism (OCD see reference 1), which can be used to determine the orientation of a-helices with respect to the plane of the membrane. This method is simple and easy to use compared with, for example, the NMR method, which requires isotope labeled samples. Indeed, it is the ease of this method that allowed us to examine alamethicin in many different chemical conditions and that resolved a controversial question about the nonconducting state of alamethicin and subsequently led to the discovery of a new phenomenon of amphiphilic helical peptides (2). 

The chloroplast genome is similar to that of mitochondria, reflecting its similar bacterial origin. However, the circular chromosome is larger than its mitochondrial counterpart, encoding 30 membrane proteins that are involved in photosynthesis. It also encodes the four components of the bacterial ribosomal system (23S, 16S, 5S, and 4.5S), 20 ribosomal proteins, and 30 tRNAs. Notable among the proteins is one of the subunits of ribulose bisphosphate carboxylase (Rubisco). This enzyme catalyzes the carboxylation of ribulose 1,5-bisphosphate from COj and is responsible for carbon fixation in plants. It is the most abimdant protein on earth. 

At least 12 genes are involved in the formation of nitrate reductase in various Enterobacteriaceae, 5 nar genes have been identified in Pseudomonas aeruginosa and 13 Chi mutations have been characterized in Bacillus licheniformis (Stouthamer, 1976). The physiological properties of chlorate-resistant mutants have been characterized and their location on the circular chromosome determined. Chi mutations have a pleotropic affect such characteristics as dehydrogenase activity, cytochrome distribution, and membrane protein composition may be influenced. The different Cfi/ mutants are able to synthesize various components of the complex nitrate reductase molecule. It is possible, in some instances, to form active enzyme by mixing components extracted from the appropriate mutants (Stouthamer, 1976). 

Replication site the site of DNA replication in vivo. In bacteria, the R.s. is on the cell membrane. The circular DNA is bound to the cell membrane at its initiation region, together with DNA-polymerase and initiation proteins. See Deoxyribonucleic acid. 

The Danielli-Davson model has been modified by Wallach and Zahler (1966) who demonstrated by optical rotatory dispersion and circular dichroism techniques that a substantial amount of membrane protein exists in a helical conformation as opposed to random coil It is envisioned that hydrophilic portions of membrane protein are located on both sides of the membrane and are connected by hydrophobic microtubules. Lenard and Singer (1966) also advanced similar views and suggested that subunits could result from this model which, when assembled in two dimensions, could form a membrane. 

In particular, conformational changes in membrane proteins have been observed by means of circular dichroism upon addition of anesthetics. Anesthetics induce a decrease of intensity of the negative dichroic bands in the region of 224-208 nm (indicative of loss of... 

The other enzymes necessary for these processes are peripheral or integral inner membrane proteins. The matrix contains discrete double-helical strands of circular DNA and ribosomes. Unlike nuclear DNA, mitochondrial DNA is not complexed with protein. The majority of mitochondrial proteins... 

A major component of biological membranes is protein. In characterizing membrane proteins, the first line of investigation has been to identify their enzymatic activities. However, with the use of solubilizing agents such as SDS and the development of amino acid analysis, gel electrophoresis, ORD, circular dichroism, and other methods, more information about structural proteins has evolved. 

The space inside the inner mitochondrial membrane is called the matrix, and it contains most of the enzymes of the TCA cycle and fatty acid oxidation. (An important exception, succinate dehydrogenase of the TCA cycle, is located in the inner membrane itself.) In addition, mitochondria contain circular DNA molecules, along with ribosomes and the enzymes required to synthesize proteins coded within the mitochondrial genome. Although some of the mitochondrial proteins are made this way, most are encoded by nuclear DNA and synthesized by cytosolic ribosomes. 

The protein-containing colloidal solutions of water-in-organic solvents are optically transparent. Hence, absorption spectroscopy, circular dichroism spectroscopy and fluorescence spectroscopy are found to be convenient for studying biocatalysis [53]. The reversed micelles are interesting models for studying bioconversion, since the majority of the enzymes in vivo act inside or on the surface of biological membranes. 

Figure 5.16 Illustration of the manner by which the virion of a filamentous single-stranded phage (such as M13 or fd) leaves an infected cell without lysis. The A protein passes first through the membrane at a site on the membrane where coat protein molecules have first become imbedded. The intracellular circular DNA is coated with dimers of another protein, gp5, which is displaced by coat protein as the DNA passes through the intact membrane.

Bacteria normally harbour a single, circular chromosome that tends to be tethered to the bacterial plasma membrane and tends to have few if any closely associated proteins. Many bacteria also contain extra-chromosomal DNA in the form of plasmids, as will be discussed later. Eukaryotes (plants, animals and yeasts) posses multiple linear chromosomes contained within a cell nucleus, and these chromosomes are normally closely associated with proteins termed histones (the pro-tein-DNA complex is termed chromatin). Eukaryotes also invariably possess DNA sequences within mitochondria and in chloroplasts in plants. The (usually circular) DNA molecules are much... 

Cyclotides, circular mini-proteins bearing a cystine knot motif, are produced by plants as part of their defense mechanism. These cyclic proteins are thermostable and were recently shown to disrupt the membrane of human lymphoma cell line HeLa, causing cellular leakage. The combined approach growth- and non-growth-associated pattern provided the accumulation of 370-mg cyclotide kalata Bl/gdw within Oldenlandia affinis cells in culture. " ... 

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