Mesp1 Patterns Mesoderm into Cardiac,Hematopoietic, or Skeletal Myogenic Progenitors in a Context-Dependent Manner

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Conformational analysis of the dipeptide taste ligand L-aspartyl-D-2-aminobutyric acid-(S)-α-ethylbenzylamide and its analogues by NMR spectroscopy,computer simulations and X-ray diffraction studies

A dipeptide taste ligand L -aspartyl-D -2-aminobutyric acid-(S)-α-ethylbenzylamide was found to be about 2000 times more potent than sucrose. To investigate the molecular basis of its potent sweet taste, we carried out conformational analysis of this molecule and several related analogues by NMR spectroscopy, computer simulations and X-ray crystallographic studies. The results of the studies support our earlier model that an ‘L’-shape molecular array is essential for eliciting sweet taste. In addition, we have identified an aromatic group located between the stem and the base of the ‘L-shape’, which is responsible for enhancement of sweetness potency. In this study, we also assessed the optimal size of the essential hydrophobic group (X) and the effects of the chirality of the second residue toward taste. ©1997 European Peptide Society and John Wiley & Sons, Ltd.     

Conformational characterization of peptides rich in the cycloaliphatic Cα,α-disubstituted glycine 1-amino-cyclononane-1-carboxylic acid

A series of N- and C-protected, monodispersed homo-oligopeptides (to the pentamer level) from the cycloaliphatic C^α,α,-dialkylated glycine 1-aminocyclononane-1-carboxylic acid (Ac₉c) and two Ala/Ac₉c tripeptides have been synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and ¹H-NMR. The molecular structures of the amino acid derivatives mClAc-Ac₉c-OH and Z-Ac₉c-OtBu, the dipeptide pBrBz-(Ac₉c)₂-OtBu, the tetrapeptide Z-(Ac₉c)₄-OtBu, and the pentapeptide Z-( Ac₉c)₅-OtBu were determined in the crystal state by X-ray diffraction. Based on this information, the average geometry and the preferred conformation for the cyclononyl moiety of the Ac₉c residue have been assessed. The backbone conformational data are strongly in favour of the conclusion that the Ac₉c residue is a strong β-turn and helix former. A comparison with the structural propensity of α-aminoisobutyric acid, the prototype of C^α,α-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Ac_nc, with n=3−8) is made and the implications for the use of the Ac₉c residue in conformationally constrained analogues of bioactive peptides are briefly examined. © 1997 European Peptide Society and John Wiley & Sons, Ltd. J. Pep. Sci. 3: 367–382 No. of Figures: 10. No. of Tables: 6. No. of References: 62     

Mitochondrial DNA instability mutants of the bifunctional protein Ilv5p have altered organization in mitochondria and are targeted for degradation by Hsp78 and the Pim1p protease

Ilv5p is a bifunctional mitochondrial protein in Saccharomyces cerevisiae required for branched-chain amino acid biosynthesis and for the stability of wild-type (rho(+)) mitochondrial DNA (mtDNA). Mutant forms of Ilv5p defective in mtDNA stability (a(+)D(-)) are present as 5-10 punctate structures in mitochondria, whereas mutants lacking enzymatic function (a(-)D(+)) show a reticular distribution, as does wild-type Ilv5p. a(+)D(-) ilv5 mutations are recessive, and the mutant protein is redistributed to a reticular form when co-expressed with wild-type Ilv5p. Ilv5p proteins that are punctate in vivo are also less soluble in detergent extracts of isolated mitochondria, suggesting that the punctate foci in a(+)D(-) Ilv5p mutants are aggregates of the protein. a(+)D(-) Ilv5p proteins are selectively degraded in cells lacking a functional mitochondrial genome, but only in cells grown under derepressing conditions. The targeted degradation of a(+)D(-) Ilv5p, which occurs even when co-expressed with wild-type Ilv5p, is mediated by the glucose-repressible chaperone, Hsp78, and by the ATP-dependent Pim1p protease, whose activity may be modulated by rho(+) mtDNA.     

Effect of lengthening of peptide backbone by insertion of chiral beta-homo amino acid residues: conformational behavior of linear peptides containing alternating L-leucine and beta-homo L-leucine residues

The synthesis and the solution behavior of the linear peptides containing a beta-homo (beta-H) leucine residue-Boc-Leu-beta-HLeu-Leu-OMe, Boc-beta-HLeu-Leu-beta-HLeu-Leu-OMe, and Boc-Leu-beta-HLeu-Leu-beta-HLeu-Leu-OMe-as well as the solid structure of the tripeptide, are reported. The conformational behavior of the peptides was investigated in solution by two-dimensional nmr. Our data support the existence in solution with different families of conformers in rapid interchange. The crystals of the tripeptide are orthorhombic, space group P2(1)2(1)2, with a = 15.829(1) A, b = 29.659(1) A, c = 6.563(1) A, and Z = 4. The structure has been solved by direct methods and refined to final R1 and wR2 indexes of 0.0530 and 0.1436 for 2420 reflections with I > 2sigma(I). In the solid state, the tripeptide does not present intramolecular H bonds, and the peptide backbone of the two leucine residues adopts a quasi-extended conformation. For the beta-HLeu residue, the backbone conformation is specified by the torsion angles straight phi(2) = -120.9(4) degrees, mu(2) = 56.7(4) degrees, psi(3) = -133.2(4) degrees. The side chains of the three residues assume the same conformation (g(-), g(-), trans), and all peptide bonds, except the urethane group at the N-terminus, are in the trans conformation. Preliminary conformational energy calculations carried out on the Ac-NH-beta-HAla-NHMe underline that the conformations with mu angle equal to 180 degrees and 60 degrees assume lower energy with respect to the others. In addition, we found a larger conformational freedom for the psi angle with respect to the straight phi angle.