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 / 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 Å 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 ␤-sheet. The N terminus forms a ␤-strand, followed by a large stretch comprising three ␣-helices. A loop region containing a short ␤-strand separates these helices from a fourth ␣-helix. The C terminus consists of two more ␤-strands completing the four-stranded antiparallel ␤-sheet with strand order 2143. Interestingly, the third ␤-strand includes a Gly-Pro cis peptide bond. The curved ␤-strand forms a hydrophobic binding pocket together with ␣-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.Keywords: protein structure; NMR; parvulin; PPIase; cis peptide bond Parvulins represent the most recently discovered third protein family within the enzyme class of peptidyl prolyl cis/ trans isomerases (PPIases, EC 5.2.1.8). These enzymes accelerate the adjustment of the cis/trans equilibrium of peptidyl-prolyl bonds in peptides and proteins (Fischer 2000). The Escherichia coli Par10 embodies the archetype of the homonymous protein family, and defines the minimal catalytic domain of the whole body of parvulin-like enzymes. Par10 was originally identified by its enzymatic activity in Reprint requests to: Gerd Gemmecker, Department Chemie, OC II, TU München, Lichtenbergstr. 4, D-85747 Garching, Germany; e-mail: Gerd. Gemmecker@ch.tum.de; fax: +49 (89) 289 13210.Abbreviations: ARIA, ambiguous restraints in iterative assignment; CNS, crystallography and NMR system; CSI, chemical shift index; DTE, dithioerythrol; EDTA, ethylendiamine tetraacetate; HSQC, heteronuclear single-quantum correlation; isopropyl ß-D-thiogalactopyranoside (IPTG); MEXICO, measurement of exchange in isotopically labelled compounds; RMSD, root mean square deviation.Article and publication are at

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.

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