NMR studies reveal structural differences between the gallium and yttrium complexes of DOTA-D-Phe1-Tyr3-octreotide.

The somatostatin analogue DOTATOC, DOTA-[Tyr(3)]octreotide, is used for in vivo diagnosis and targeted therapy of somatostatin-receptor-positive tumors. DOTATOC consists of a disulfide-bridged octapeptide, d-Phe(1)-Cys(2)-Tyr(3)-d-Trp(4)-Lys(5)-Thr(6)-Cys(7)-Thr(8)-ol, connected to the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). Two metal complexes, Ga(III)- and Y(III)-DOTATOC, were reported to differ significantly in somatostatin receptor affinity and tumor uptake. Our (1)H and (13)C solution NMR data and modeling studies of both compounds are in agreement with a fast conformational equilibrium of the peptide part, as previously reported for octreotide itself. However, the different coordination geometry of Ga(3+) and Y(3+) (6-fold and 8-fold, respectively, as known from model compounds) causes pronounced differences for the d-Phe(1) residue. For Y(III)-DOTATOC this leads to two conformers exchanging slowly on the NMR time scale. From various NMR measurements, they could be identified as cis-trans isomers at the amide bond between DOTA chelator and first residue (d-Phe(1)H(N)) of the peptide.

Solution structure of Escherichia coli Par10: The prototypic member of the Parvulin family of peptidyl-prolyl cis/trans isomerases.

E. coli Par10 is a peptidyl-prolyl cis/trans isomerase (PPIase) from Escherichia coli catalyzing the isomerization of Xaa-Pro bonds in oligopeptides with a broad substrate specificity. The structure of E. coli Par10 has been determined by multidimensional solution-state NMR spectroscopy based on 1207 conformational constraints (1067 NOE-derived distances, 42 vicinal coupling-constant restraints, 30 hydrogen-bond restraints, and 68 phi/psi restraints derived from the Chemical Shift Index). Simulated-annealing calculations with the program ARIA and subsequent refinement with XPLOR yielded a set of 18 convergent structures with an average backbone RMSD from mean atomic coordinates of 0.50 A within the well-defined secondary structure elements. E. coli Par10 is the smallest known PPIase so far, with a high catalytic efficiency comparable to that of FKBPs and cyclophilins. The secondary structure of E. coli Par10 consists of four helical regions and a four-stranded antiparallel beta-sheet. The N terminus forms a beta-strand, followed by a large stretch comprising three alpha-helices. A loop region containing a short beta-strand separates these helices from a fourth alpha-helix. The C terminus consists of two more beta-strands completing the four-stranded anti-parallel beta-sheet with strand order 2143. Interestingly, the third beta-strand includes a Gly-Pro cis peptide bond. The curved beta-strand forms a hydrophobic binding pocket together with alpha-helix 4, which also contains a number of highly conserved residues. The three-dimensional structure of Par10 closely resembles that of the human proteins hPin1 and hPar14 and the plant protein Pin1At, belonging to the same family of highly homologous proteins.

Design, synthesis, and NMR structure of linear and cyclic oligomers containing novel furanoid sugar amino acids.

Sugar Amino Acids (SAAs) are sugar moieties containing at least one amino and one carboxyl group. The straightforward synthesis of two furanoid SAAs, 3-amino-3-deoxy-1,2-isopropylidene-alpha-D-ribofuranoic acid (f-SAA1) and 3-amino-3-deoxy-1,2-isopropylidene-alpha-D-allofuranoic acid (f-SAA2) starting from diacetone glucose, is described. These SAAs were used as structural templates aiming at new structures for peptidomimetic drug design. f-SAA1 resembles a beta-amino acid, whereas f-SAA2 is a gamma-amino acid mimetic. Thus, for the synthesis of the mixed, linear and cyclic oligomers of f-SAA1, beta-homo-glycine (beta-hGly, also called beta-alanine) was chosen as an amino acid counterpart, while for the oligomer of f-SAA2 gamma-amino butyric acid (GABA) was chosen. Fmoc-[f-SAA1-beta-hGly](3)-OH (3) and cyclo[f-SAA1-beta-hGly](3) (5) resemble linear and cyclic beta-peptides with a very different substitution pattern, compared with the beta-peptides known so far in the literature, whereas Fmoc-[f-SAA2-GABA](3)-OH (4) resembles a gamma-peptide. The linear f-SAA oligomers 3 and 4 were synthesized on the solid-phase using Fmoc strategy. 23 unambiguous interresidue NOE contacts (from a total of 76 NOE values), obtained from extensive NMR studies in C(3)CN, were used in subsequent simulated annealing and MD calculations, to elucidate the 12/10/12-helical structure of oligomer 3 in CH(3)CN. The results indicate that f-SAA1 strongly induces a secondary structure. A characteristic CD curve for the linear oligomer 3 is observed up to 75 degrees C in both CH(3)CN and CH(3)CN/H(2)O, even though 3 contains beta-hGly, which is known to destabilize helices. By contrast, 4 does not seem to form a stable conformation in solution. The cyclic SAA containing oligomer cyclo [f-SAA1-beta-hGly](3) (5) exhibits a C(3) symmetric conformation on the NMR chemical shift time scale.

Synthesis and NMR studies of cyclopeptides containing a sugar amino Acid.

[structure: see text] Cyclopeptides containing Glucuronic acid methylamine (Gum) alternating with Gly, L-Ala, D-Ala, L-Phe, D-Phe, L-Lys, or D-Lys were synthesized by a combination of solid-phase synthesis and solution chemistry. A more effective pathway to synthesize the sugar amino acid Gum in higher yields and in a shorter period of time was developed. Gum is employed in the benzylated and deprotected form. The cyclopeptides were characterized by NMR and the structure of one deprotected cyclic peptide solved.