ABSTRACT
To provide stable and low-cost naturally derived yellow pigments, a variety of food byproducts were evaluated and the constituents of lemon peel have emerged yielding a highly promising natural product with applications as a food dye. Here we report a new, highly stable and water soluble food dye called yellow #15 from the ethanol extract of the zest of Citrus limon. The structure of lemon yellow #15 was carefully assigned on the basis of spectroscopic data, including 1D and 2D NMR spectroscopy, and the absolute configuration was established by comparison of the experimental CD with calculated electronic circular dichroism (ECD) spectral data. CIELAB values and Delta CIELAB were measured and revealed this new water-soluble pigment has superior light stability relative to other natural products used as food dyes.
Subject(s)
Citrus/chemistry , Food Coloring Agents , Food , Plant Extracts/chemistry , WaterABSTRACT
Improved methodologies are provided to synthesize (1R,2S)-2-aminocyclobutane-1-carboxylic acid derivatives and their incorporation into beta-peptides of 2-8 residues bearing different N-protecting groups. The conformational analysis of these oligomers has been carried out by using experimental techniques along with theoretical calculations. This study shows that these oligomers adopt preferentially a strand-type conformation in solution induced by the formation of intra-residue six-membered hydrogen-bonded rings, affording cis-fused [4.2.0]octane structural units that confer high rigidity on these beta-peptides. Moreover, all of them are prone to self-assemble producing nano-sized fibres, as evidenced by TEM, AFM and SPFM, and, in some instances, they also form gels. These techniques and molecular modelling allowed us to suggest an aggregation model for the assembly structures in which a parallel molecular-arrangement is preferred and the conformation is similar to that observed in solution. According to this model, both hydrogen-bonding and hydrophobic interactions would account for formation of the assemblies.
Subject(s)
Amino Acids, Cyclic/chemistry , Oligopeptides/chemistry , Protein Folding , Circular Dichroism , Hydrolysis , Magnetic Resonance Spectroscopy , Microscopy , Molecular Dynamics Simulation , Oligopeptides/chemical synthesis , Protein Conformation , Solutions , StereoisomerismABSTRACT
Amyloids are a family of self-aggregating proteins implicated in various central nervous system disorders, including Alzheimer's disease (AD). It is thought that prefibrillar soluble forms of amyloid peptides, including oligomers, may be the main pathogenic factor in AD. Herein we describe the fabrication of well-defined, functionalized, monomeric beta-amyloid peptide surfaces for studying protein-protein interactions. We first prepared a nonaggregating analogue of the beta-amyloid peptide and then attached it to a gold surface covered with a self-assembled monolayer (SAM) of alkanethiols. After attachment, the native form of the beta-amyloid peptide (Abeta40) was obtained by surface-level intramolecular O-N migration. The surface was characterized by atomic force microscopy (AFM) and self-assembled monolayer for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (SAMDI-TOF MS). The interaction between the surface-bound Abeta40 and monoclonal anti-Abeta40 antibody was tracked by AFM and chemiluminescence, which revealed that the Abeta40 was attached mainly in its monomeric form and that the protein-protein complex was assembled on the surface. Last, we used a proteomics approach to demonstrate the specificity of the Abeta40-functionalized surface in surface-binding experiments employing serum amyloid P (SAP) and bovine serum albumin (BSA).
Subject(s)
Amyloid beta-Peptides/chemistry , Gold/chemistry , Nitrogen/chemistry , Oxygen/chemistry , Peptide Fragments/chemistry , Amino Acid Sequence , Amyloid beta-Peptides/chemical synthesis , Amyloid beta-Peptides/metabolism , Animals , Cattle , Humans , Molecular Sequence Data , Peptide Fragments/chemical synthesis , Peptide Fragments/metabolism , Serum Albumin, Bovine/chemistry , Serum Albumin, Bovine/metabolism , Serum Amyloid P-Component/chemistry , Serum Amyloid P-Component/metabolism , Surface PropertiesABSTRACT
A beta-tetrapeptide made up of homochiral cyclobutane residues displays conformational bias in solution prompted by the formation of intramolecular hydrogen bonds. Moreover, this compound self-assembles to produce nanosized fibrils and, in some media, it also forms a gel. The combination of NMR, TEM, AFM, and theoretical calculations has proven to be very useful in obtaining insight into the details of these new structures.
Subject(s)
Cyclobutanes/chemistry , Nanostructures/chemistry , Oligopeptides/chemistry , Hydrogen Bonding , Magnetic Resonance Spectroscopy , Microscopy, Atomic Force , Microscopy, Electron, Transmission , Oligopeptides/chemical synthesis , Solutions/chemistryABSTRACT
The first hemoglobin (Hb) variant carrying a mutation at beta4 was identified as beta4(A1)Thr-->Asn or Hb Würzburg and constituted 38% of the total hemoglobin. It showed a slightly elevated oxygen affinity and a slightly decreased cooperativity index (n50 = 2.3 versus n50 = 2.8). The analysis of the electrostatic potential showed an increased negative charge at the site of the mutation with a displacement of beta6(A3)Glu by 1.3A. The replacement of threonine by asparagine seems to stabilize the R conformation. This may explain partially both the high affinity and the reduction in cooperativity.
Subject(s)
Diabetes Mellitus, Type 2/blood , Hemoglobins, Abnormal/chemistry , Spectrometry, Mass, Electrospray Ionization/methods , Amino Acid Substitution , DNA/chemistry , Female , Hemoglobins, Abnormal/genetics , Humans , Middle Aged , Models, Molecular , Spectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationABSTRACT
TFIIH is a multiprotein complex that plays a central role in both transcription and DNA repair. The subunit p62 is a structural component of the TFIIH core that is known to interact with VP16, p53, Eralpha, and E2F1 in the context of activated transcription, as well as with the endonuclease XPG in DNA repair. We used limited proteolysis experiments coupled to mass spectrometry to define structural domains within the conserved N-terminal part of the molecule. The first domain identified resulted from spontaneous proteolysis and corresponds to residues 1-108. The second domain encompasses residues 186-240, and biophysical characterization by fluorescence studies and NMR analysis indicated that it is at least partially folded and thus may correspond to a structural entity. This module contains a region of high sequence conservation with an invariant FWxxPhiPhi motif (Phi representing either tyrosine or phenylalanine), which was also found in other protein families and could play a key role as a protein-protein recognition module within TFIIH. The approach used in this study is general and can be straightforwardly applied to other multidomain proteins and/or multiprotein assemblies.
