Multiprotein assembly

Topographs of the subsolubilizing concentration detergent-treated photosynthetic membranes in R sphaeroides derived from oscillatingmode AFM in aqueous condition revealed a relatively ordered network of both LH2 and dimeric RC-LHl core complexes (Fig. 17.6B). The dimeric RC-LHl core complexes formed linear arrays of up to six dimers. The specific core organization may allow the LHl excitation to migrate along a series of dimers until 

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Jerng, H.H., Kunjilwar, K., and Pfaffinger, P.J. (2005) Multiprotein assembly of Kv4.2, KChIP3 and DPP10 produces ternary channel complexes with ISA-like properties./. Physiol. 568, 767-788. 

In contrast, methylation at K4 of H3 is correlated with transcriptionally active states of chromatin. The K4 methylation appears to be absent from histones with methylation at K9, but colocalizes with acetylation at K9, indicating a positive cooperation of acetylation and methylation of distinct Lys residues during the establishment of a transcriptionally active state. For yeast histones, a link between methylation and acetylation at Lys residues and phosphorylation at Ser residues of histone H3 has been discovered (Nakayamaet al.,., 2001), defining a conserved pathway of sequential histone modifications during heterochromatin assembly. These modifications are recognized by specific proteins that are part of multiprotein assemblies in heterochromatin. 

Saunders, M. G., and G. A. Voth, Coarse-graining of multiprotein assemblies. Current Opinion in Structural Biology, 2012.22(2) pp. 144-150,... 

Saunders, M.G., Voth, G.A. Coarse-graining of multiprotein assemblies. Curr. Opin. Struct. Biol. 22, 144-150 (2012)... 

Peptides and proteins do not carry out their biological functions in isolation. Their active forms may be associated with metal ions, small molecules, macromolecules including proteins and DNA, and they may form complex multiprotein assemblies. Biological processes occur in aqueous solution in the presence of salts and other ions whereas MS is used to probe substances isolated in vacuo conditions that could be incompatible. Despite this, the use of MS to study these interactions is growing rapidly. MALDI, which ionizes directly from the solid phase, does not lend itself to studies that mirror solution conditions, but ESI, which abstracts ions directly from solution by rapid evaporation of nebulized droplets, can monitor noncovalent associations very successfully. 

Once integrated into the host chromosome, the assembly of new viral particles necessitates the prodnction of viral RNA transcripts and proteins. Initiation of viral transcription is also an RNA independent process where host transcription promoters and enhancer elements such as NF-kB bind to the 5 -LTR. The host transcriptional complex is then recrnited and transcription commences.Once transcription has been initiated, RNA and RNA-RNA interactions play a critical role in mediating the production of viral transcripts. The multiprotein transcription complex has a recognition factor for nonhost DNA and quickly releases from viral DNA, creating short, abortive transcripts. Processing and nuclear export of these transcripts leads to the translation of the HIV Tat protein, a small early-phase viral protein (Figure 10.4) that plays a key role in the ultimate formation of fnll-length viral RNA transcripts. 

Histone acetyltransferases (HATs) are enzymes that acetylate specific lysine residues in histones through the transfer of an acetyl group from an acetyl-coenzymeA (AcCoA) molecule, causing profound effects on chromatin structure and assembly as well as gene transcription. HATs are found in most, if not all, eukaryotic organisms as multiprotein complexes, some HAT catalytic subunits even being shared between various complexes that display different substrate specificities based on their subunit composition [12]. Despite their name, HATs do not restrict themselves to the acetylation of histones, since these enzymes have also been shown to act on nonhistone proteins, broadening their scope of action [13]. 

One point to address concerns the use of the words s pramolecular and supermolecule. The concept of supramolecular chemistry has become a unifying attractor, in which areas that have developed independently have spontaneously found their place. The word supramolecular has been used in particular for large multiprotein architectures and organized molecular assemblies [1.16]. On the other hand, in theoretical chemistry, the computational procedure that treats molecular associations such as the water dimer as a single entity is termed the supermolecule approach [1.34,1.35]. Taking into account the existence and the independent uses of these two words, one may then propose that supramolecular chemistry be the broader term, concerning the chemistry of all types of supramolecular entities from the well-defined supermolecules to extended, more or less organized, polymolecular associations. The term super molecular chemistry would be restricted to the specific chemistry of the supermolecules themselves. 

To the extent that they are covalently linked, the complex polyketide synthases are less reliant on association for function. In most systems, however, transient docking between multienzymes is required. Recently, it has been demonstrated that the regions of sequence upstream from N-terminal modules and downstream from C-terminal modules (referred to as interpolypeptide linkers) play a crucial role in the assembly of functional modules in vivo [78]. Clearly, the presence of such linkers will also be important for productive biosynthesis in vitro using multiprotein systems. 

Hydrophobic and osmophobic effects are important not only in the folding of individual polypeptide chains into compact globular proteins, but also in the assembly of multiprotein complexes. Osmophobic effects are noted, for instance, in the self-assembly of subunits of the glycolytic enzyme phosphofructokinase (PFK). Self-assembly is enhanced by the presence of stabilizing organic cosolvents such as trimethylamine-A-oxide (TMAO) (Hand and Somero, 1982). As discussed later, self-assembly driven by osmophobic effects results from the thermodynamic favorability of minimizing the surface area on the proteins that is in contact with the cosolvent. 

Vondriska, T.M., Pass, J.M. and Ping, P. (2004) Scaffold proteins and assembly of multiprotein signaling complexes. J. Mol. Cell Cardiol. 37, 391-397. 

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