Accessory protein

The main structural differences between procapsids and mature capsids are a result of the reconfiguration of the capsid shell and loss of scaffold described above. However, both T4 and HSV-1 encode additional proteins 

In both T4 and HSV-1 the maturation of the capsid shell is necessary for DNA packaging. In HSV-1 the sequence of events during packaging is not known but in T4 packaging is initiated into unexpanded heads, although head expansion is necessary to allow packaging of the complete genome (Jardine and Coombs, 1998 Jardine et al, 1998). Because in both viruses 

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Biological targets may consist of single-entity proteins, complexes of receptors (dimers), or receptors plus accessory proteins. Mixtures of gene products can produce unique phenotypic biological targets. 

Foord, S. M., and Marshall, F. H. (1999). RAMPS Accessory proteins for seven transmembrane domain receptors. Trends Pharmacol. Sci. 20 184-187. 

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

Figured. Diagrammatic representation of the red blood cell cytoskeletal-plasma membrane complex. Spectrin is made up of many homologous triple-helical segments joined by nonhelical regions (Speicher and Marchesi, 1984). Spectrin and actin require accessory proteins to form a membrane-associated network. (This diagram is constructed from data previously published for example, see Stryer, 1988 Davies and Lux, 1989 Bennett and Gilligan, 1993).

Muscle contraction is initiated by a signal from a motor nerve. This triggers an action potential, which is propagated along the muscle plasma membrane to the T-tubule system and the sarcotubular reticulum, where a sudden large electrically excited release of Ca " into the cytosol occurs. Accessory proteins closely associated with actin (troponins T, I, and C) together with tropomyosin mediate the Ca -dependent motor command within the sarcomere. Other accessory proteins (titin, nebulin, myomesin, etc.) serve to provide the myofibril with both stability... 

In a previous section we mentioned the significance of myosin filament structure. In nematodes two forms of myosin-II, myosin A and B, are required for proper filament stmcture (Epstein, 1988). The two forms of myosin are expressed at the proper time to allow for correct filament assembly. An accessory protein called paramyosin is also required for correct filament assembly. In vertebrate cardiac muscle, there are also two isoforms of myosin-II a-myosin and p-myosin. The proper ratio of these two proteins is of utmost importance for proper muscle activity. The incorrect synthesis of a- and P-myosins results in a severe cardiac disorder known as hypertrophic cardiomyopathy. Genetic transmission of the disease occurs in about 55% of families. The inherited condition is called familial hypertrophic cardiomyopathy (FHC), and this condition is a leading cause of sudden death in young athletes. 

The ion channel receptors are relatively simple in functional terms because the primary response to receptor activation is generated by the ion channel which is an integral part of the protein. Therefore, no accessory proteins are needed to observe the response to nicotinic AChR activation and the full functioning of the receptor can be observed by isolating and purifying the protein biochemically and reconstituting the protein in an artificial lipid membrane. In contrast, the G-protein-coupled receptors require both G-proteins and those elements such as phospholipase-C illustrated in Fig. 3.1, in order to observe the response to receptor activation (in this case a rise in intracellular calcium concentration resulting from the action of IP3 on intracellular calcium stores). 

Nucleosomes can be reconstructed in the laboratory from DNA and pure histones. Histone HI is not necessary for the reconstruction, which further shows that HI is an accessory protein and not a major structural part of the nucleosome subunit. 

Schug, A. Herges, T. Wenzel, W., All-atom folding of the three-helix HIV accessory protein with an adaptive parallel tempering method, Proteins-Struct. Funct. Bioinform. 2004, 57, 792-798... 

Crespi, C. L., Greenblatt, D. J., Comparison between cytochrome P450 (CYP) content and relative activity approaches to scaling from cDNA-expressed CYPs to human liver microsomes ratios of accessory proteins as sources of discrepancies between the approaches, Drug Metab. Dispos. 2000, 28, 1493-1504. 

DMS also has been used to study the interaction between the Helicobacter pylori accessory proteins HypA and UreE (Benoit et al., 2007) as well as to identify the interaction between the Ca2+-binding protein S100A11 and the Ca2+- and phospholipid-binding protein annexin A6 (Chang et al., 2007). 

Benoit, S.L., Mehta, N., Weinberg, M.V., Maier, C., and Maier, R.J. (2007) Interaction between the Helicobacter pylori accessory proteins HypA and UreE is needed for urease maturation. Microbiology 153,1474-1482. 

Glazer, A.N. (1981) Photosynthetic accessory proteins with bilin prosthetic groups. Biochem. Plants 8, 51-96. 

V Proaccelerin Both Accessory protein, enhances rate of activation of X... 

VIII Antihaemophilic factor Intrinsic Accessory protein, enhances activation of X (intrinsic system)... 

Blumer, J. B. and Lanier, S. M. Accessory proteins for G protein-signaling systems activators of G protein signaling and other nonreceptor proteins influencing the activation state of G proteins. Receptors Channels 9 195-204, 2003. 

N. Drapal, A. Bock (1998) Interaction of the hydrogenase accessory protein HypC with HycE, the large subunit of Escherichia coli hydrogenase 3 during enzyme maturation. Biochemistry, 37 2941-2948... 

Taylor There has been quite a conflicting literature on whether accessory proteins might be involved in mediating some of these Ca2+ effects on L1SP3 receptors, and lots of bilayer recordings have failed to find inhibitory effects of Ca2+. Can you comment on this ... 

The development of biological tools to support DDI studies has paralleled the development of bioanalytical techniques. To better understand in vitro-in vivo (IVIV) correlations, the effects of differences in enzyme preparations and incubation conditions must be understood. Differences between enzyme preparations include nonspecific binding, the ratio of accessory proteins (cytochrome b5 and reductase) to CYPs and genetic variability differences in incubation conditions include buffer strength, the presence of inorganic cations and solvent effects. Understanding how biology influences enzymatic activity is crucial to accurate and consistent prediction of the inhibition potential. 

Figure 9.3 The effects of varying levels of accessory proteins on CYP2C9 kinetics using diclofenac (a) or (S)-warfarin (b) as substrate probe [219].

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