Home About us Contact
|
Home About us Contact | ||
|
|
||
Residue Interactions (residue + interaction)
Selected AbstractsRetrograde melt,residue interaction and the formation of near-anhydrous leucosomes in migmatitesJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2010R. W. WHITE Abstract Considering physical segregation of melt from its residue, the chemical potentials of the components (oxides) are the same in both when segregation occurs. Then, as P,T conditions change, gradients in chemical potential are established between the melt-rich domains and residue permitting diffusional interaction to occur. In particular, on cooling, the chemical potential of H2O becomes higher in the melt segregation than in the residue, particularly when biotite becomes stable in the residue assemblage. Diffusion of water from the melt to the residue promotes crystallization of anhydrous products from the melt and hydrous products in the residue. This diffusive process, when coupled with melt loss from the rocks subsequent to some degree of crystallization, can result in a significant degree of anhydrous leucosome being preserved in a migmatite with only minor retrogression of the residue. If H2O can diffuse between the melt segregation and all of the residue, then no apparent selvedge between the two will be observed. Alternatively, if H2O can diffuse between the melt segregation and only part of the residue, then a distinct selvedge may be produced. Diffusion of H2O into the residue may be in part responsible for the commonly anhydrous nature of leucosomes, especially in granulite facies migmatites. Diffusion of other relatively mobile species such as Na2O and K2O has a lesser effect on overall melt crystallization but can change the proportion of quartz, plagioclase and K-feldspar in the resultant leucosome. The diffusion of H2O out of the melt results in the enhanced crystallization of the melt in the segregation and increases the amount of resulting anhydrous leucosome relative to the amount produced if melt crystallized in chemical isolation from the residue. For high residue:melt ratios, the proportion of resulting near-anhydrous leucosome can approach that of the proportion of melt present at the onset of cooling with only minor loss of melt from a given segregation required. Crystallization of melt segregations via the diffusion of H2O out of them into the host may also play a major role in driving melt-rich segregations across key rheological transitions that would allow the expulsion of remaining melt from the system. [source] Crystal structures of truncated alphaA and alphaB crystallins reveal structural mechanisms of polydispersity important for eye lens functionPROTEIN SCIENCE, Issue 5 2010Arthur Laganowsky Abstract Small heat shock proteins alphaA and alphaB crystallin form highly polydisperse oligomers that frustrate protein aggregation, crystallization, and amyloid formation. Here, we present the crystal structures of truncated forms of bovine alphaA crystallin (AAC59,163) and human alphaB crystallin (ABC68,162), both containing the C-terminal extension that functions in chaperone action and oligomeric assembly. In both structures, the C-terminal extensions swap into neighboring molecules, creating runaway domain swaps. This interface, termed DS, enables crystallin polydispersity because the C-terminal extension is palindromic and thereby allows the formation of equivalent residue interactions in both directions. That is, we observe that the extension binds in opposite directions at the DS interfaces of AAC59,163 and ABC68,162. A second dimeric interface, termed AP, also enables polydispersity by forming an antiparallel beta sheet with three distinct registration shifts. These two polymorphic interfaces enforce polydispersity of alpha crystallin. This evolved polydispersity suggests molecular mechanisms for chaperone action and for prevention of crystallization, both necessary for transparency of eye lenses. [source] Ligand-induced activation of the insulin receptor: a multi-step process involving structural changes in both the ligand and the receptorBIOESSAYS, Issue 4 2009Colin W. Ward Abstract Current models of insulin binding to the insulin receptor (IR) propose (i) that there are two binding sites on the surface of insulin which engage with two binding sites on the receptor and (ii) that ligand binding involves structural changes in both the ligand and the receptor. Many of the features of insulin binding to its receptor, namely B-chain helix interactions with the leucine-rich repeat domain and A-chain residue interactions with peptide loops from another part of the receptor, are also seen in models of relaxin and insulin-like peptide 3 binding to their receptors. We show that these principles can likely be extended to the group of mimetic peptides described by Schäffer and coworkers, which are reported to have no sequence identity with insulin. This review summarizes our current understanding of ligand-induced activation of the IR and highlights the key issues that remain to be addressed. [source] On the Origins of Enzyme Inhibitor Selectivity and Promiscuity: A Case Study of Protein Kinase Binding to StaurosporineCHEMICAL BIOLOGY & DRUG DESIGN, Issue 1 2009Duangrudee Tanramluk Relationships between ligand binding and the shapes of the binding sites in families of homologous enzymes are investigated by comparing matrices of distances between key binding site atoms. Multiple linear regression is used to help identify key distances that influence ligand binding affinity. In order to illustrate the utility of this generic approach, we study protein kinase binding sites for ATP and the promiscuous competitive inhibitor, staurosporine. We show that the size of the gatekeeper residue and the closure between the first glycine of the GXGXXG motif and the aspartate of the DFG loop act together to promote tight binding. Our web-based tool, ,mapping analogous hetero-atoms onto residue interactions' (MAHORI), indicates that the greater the number of hydrogen bonds made by the kinase around the methylamine group of staurosporine, the tighter the binding. The conservation of surrounding atoms identified using our novel grid-based method clearly demonstrates that the most structurally conserved part of the binding site for staurosporine is the main chain of the hinge region. The critical role of interactions that are not dependent on side-chain identities is consistent with the promiscuous nature of this inhibitor. [source] Amphipathic control of the 310 -/,-helix equilibrium in synthetic peptidesCHEMICAL BIOLOGY & DRUG DESIGN, Issue 2 2001L. G. J. Hammarström Abstract: A series of short, amphipathic peptides incorporating 80% C,,C, -disubstituted glycines has been prepared to investigate amphipathicity as a helix-stabilizing effect. The peptides were designed to adopt 310 - or ,-helices based on amphipathic design of the primary sequence. Characterization by circular dichroism spectroscopy in various media (1,:,1 acetonitrile/water; 9,:,1 acetonitrile/water; 9,:,1 acetonitrile/TFE; 25 mm SDS micelles in water) indicates that the peptides selectively adopt their designed conformation in micellar environments. We speculate that steric effects from ith and ith + 3 residues interactions may destabilize the 310 -helix in peptides containing amino acids with large side-chains, as with 1-aminocyclohexane-1-carboxylic acid (Ac6c). This problem may be overcome by alternating large and small amino acids in the ith and ith + 3 residues, which are staggered in the 310 -helix. [source] | ||||||||||