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Abstract: For zeolite-type frameworks the focus has for a long time been put on producing new structures that can give optimized properties for a variety of different purposes. Many new structures have been produced on a trial and error basis. Open-framework germanates have played the role of forming many new structures as it is easier to form certain building units within the germanate system. It is time to start comparing synthesis mechanisms and building units to determine how we can control the synthesis. Here we will give an overview of some of the structures found within the open-framework germanate system and demonstrate that in order for more optimized systems to be synthesized there is a clear need for the more detailed comparison of the structural systematics of existing materials.
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Apr 2010
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Paolo
Ruzza
,
Giuliano
Siligardi
,
Arianna
Donella-deana
,
Andrea
Calderan
,
Rohanah
Hussain
,
Chiara
Rubini
,
Luca
Cesaro
,
Alessio
Osler
,
Andrea
Guiotto
,
Lorenzo A.
Pinna
,
Gianfranco
Borin
Abstract: Eukaryotic signal transduction involves the assembly of transient protein-protein complexes mediated by modular interaction domains. Specific Pro-rich sequences with the consensus core motif PxxP adopt the PPII helix conformation upon binding to SH3 domains. For short Pro-rich peptides, little or no ordered secondary structure is usually observed before binding interactions. The association of a Pro-rich peptide with the SH3 domain involves unfavorable binding entropy due to the loss of rotational freedom on forming the PPII helix. With the aim of stabilizing the PPII helix conformation in the Pro-rich HPKI decapeptide PPPLPPKPKF (P2), a series of P2 analogues was prepared, in which specific Pro positions were alternatively occupied by 4(S)- or 4(R)-4-fluoro-L-proline. The interactions of these peptides with the SH3 domain of the HPK1-binding partner HS1 were quantitatively analyzed by the NILIA-CD approach. A CD thermal analysis of the P2 analogues was performed to assess their propensity to adopt the PPII helix conformation. Contrary to our expectations, the K-d values of the analogues were lower than that of the parent peptide P2. These results clearly show that the induction of a stable PPII helix conformation in short Pro-rich peptides is not sufficient to increase their affinity toward the SH3 domain and that the effect of 4-fluoroproline strongly depends on the position of this residue in the sequence and the chirality of the substituent in the pyrrolidine ring. Copyright (c) 2006 European Peptide Society and John Wiley & Sons, Ltd.
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Jul 2006
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Abstract: The search for effective drug delivery systems is one of the major challenges in drug formulation especially for biopharmaceuticals Such as proteins, and peptide-based drugs and vaccines. A procedure has been developed whereby human serum albumin (HSA) call be Used as a delivery vehicle for these biomolecules using its role as main ratty acid carrier. Using essentially fatty acid free HSA (HSAff) it is possible to form stable complexes with lipidic chain compounds (lipo-compounds). Two lipo-compounds have been used to develop this system, a novel antimicrobial lipopeptide and gamma-amino-n-butyric acid, GABA. conjugated with an alkyl chain, lipo-GABA, in both cases C8 and C14 alkyl chain lengths were evaluated. The HAS-lipo compound complex had a mutual stabilizing effect on both the HSA and the lipo-compound. The protease enzyme study showed that the alkyl chains of these lipo-compounds bound to HSAff confer a similar if not greater biostability than caprylic acid shown by CD and importantly, the bound lipopeptide was stabilized by the HSA shown by mass spectrometry. Heat stability studies at 60 degrees C over 10 h also confirmed that the lipo-HSA complexes confer stability and provide a method of preparing sterile formulation for therapeutic use. No further increased in stability of the lipo-compounds when HSA containing fatty acid (HSAfa) Was used. With the antimicrobial lipopeptide, there was enhanced activity with HSAff formulation suggesting increased biostability and bioavailability of compounds. These finding allowed us to develop a simple and effective way of delivering lipo-compounds using fatty acid free HSA as the carrier.
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Sep 2006
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Abstract: Phospho-CDK2/cyclin A, a kinase that is active in cell cycle S phase, contains an RXL substrate recognition site that is over 40 Å from the catalytic site. The role of this recruitment site, which enhances substrate affinity and catalytic efficiency, has been investigated using peptides derived from the natural substrates, namely CDC6 and p107, and a bispeptide inhibitor in which the ?-phosphate of ATP is covalently attached by a linker to the CDC6 substrate peptide. X-ray studies with a 30-residue CDC6 peptide in complex with pCDK2/cyclin A showed binding of a dodecamer peptide at the recruitment site and a heptapeptide at the catalytic site, but no density for the linking 11 residues. Kinetic studies established that the CDC6 peptide had an 18-fold lower Km compared with heptapeptide substrate and that this effect required the recruitment peptide to be covalently linked to the substrate peptide. X-ray studies with the CDC6 bispeptide showed binding of the dodecamer at the recruitment site and the modified ATP in two alternative conformations at the catalytic site. The CDC6 bispeptide was a potent inhibitor competitive with both ATP and peptide substrate of pCDK2/cyclin A activity against a heptapeptide substrate (Ki = 0.83 nm) but less effective against RXL-containing substrates. We discuss how localization at the recruitment site (KD 0.4 ?m) leads to increased catalytic efficiency and the design of a potent inhibitor. The notion of a flexible linker between the sites, which must have more than a minimal number of residues, provides an explanation for recognition and discrimination against different substrates.
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May 2006
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Aug 2009
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Aug 2009
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Simone
Weyand
,
Tatsuro
Shimamura
,
Shunsuke
Yajima
,
Shunichi
Suzuki
,
Osman
Mirza
,
Kuakarun
Krusong
,
Liz
Carpenter
,
Nicholas G.
Rutherford
,
Jonathan M.
Hadden
,
John
O'reilly
,
Pikyee
Ma
,
Massoud
Saidjam
,
Simon G.
Patching
,
Ryan J.
Hope
,
Halina T.
Norbertczak
,
Peter C. J.
Roach
,
So
Iwata
,
Peter J. F.
Henderson
,
Alexander D.
Cameron
Diamond Proposal Number(s):
[456]
Abstract: The nucleobase–cation–symport-1 (NCS1) transporters are essential components of salvage pathways for nucleobases and related metabolites. Here, we report the 2.85-angstrom resolution structure of the NCS1 benzyl-hydantoin transporter, Mhp1, from Microbacterium liquefaciens. Mhp1 contains 12 transmembrane helices, 10 of which are arranged in two inverted repeats of five helices. The structures of the outward-facing open and substrate-bound occluded conformations were solved, showing how the outward-facing cavity closes upon binding of substrate. Comparisons with the leucine transporter LeuTAa and the galactose transporter vSGLT reveal that the outward- and inward-facing cavities are symmetrically arranged on opposite sides of the membrane. The reciprocal opening and closing of these cavities is synchronized by the inverted repeat helices 3 and 8, providing the structural basis of the alternating access model for membrane transport.
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Oct 2008
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Aug 2009
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Moritz
Hoesch
,
Matteo
D’astuto
,
Matteo
Calandra
,
Geneviève
Loupias
,
Francesco
Mauri
,
Shuyun
Zhou
,
Jeff
Graf
,
Alessandra
Lanzara
,
Nicolas
Emery
,
Claire
Hérold
,
P.
Lagrange
,
Daniel
Petitgrand
Abstract: We report measurements of phonon dispersion in CaC6 using inelastic x-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. However, on the longitudinal dispersion along the (111) axis of the rhombohedral representation, we find an unexpected anticrossing with an additional longitudinal mode, at about 11 meV. At a comparable energy, we observe also unexpected intensity on the in-plane direction. These results resolve the previous incorrect assignment of a longitudinal phonon mode to a transverse mode in the same energy range. By calculating the electron susceptibility from first principles we show that this longitudinal excitation is unlikely to be due to a plasmon and consequently can probably be due to defects or vacancies present in the sample.
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Mar 2010
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Abstract: Bacteria are abundant in many natural and engineered environments where they are thought to exert important controls on the cycling, mobility, bioavailability, and toxicity of metal contaminants. In order to probe their role in moderating the behavior of lanthanides, pH-dependent adsorption edges of 13 individual lanthanides and yttrium to the Gram-negative bacterium Pantoea agglomerans were used to generate discrete site surface complexation constants. The calculated surface complexation constants were compared with stability constants estimated using linear free energy relationships based on a number of hydroxyl-containing ligands. The experimental data suggests that lanthanide adsorption edges below pH 6.5 are consistent with adsorption to phosphate groups for the light and some of the middle lanthanides (La to Gd), whereas some of the middle and heavy lanthanides appear to favor carboxyl co-ordination (Tb to Yb), although exceptions occur in each grouping. The experimentally derived surface complexation constants for carboxyl coordination were of similar magnitude to stability constants estimated from linear free energy correlations using fulvic acid stability constants. The implication is that the adsorption of lanthanides to bacterial surfaces could be modeled reasonably well using lanthanide stability constants for natural organic matter, except perhaps at low pH where phosphate binding dominates.
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Jan 2010
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