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J Zanen

Publications and source records attributed to J Zanen.

At least 37 records · Page 2Linked to original sources
PubMed1982

The conformational properties of somatostatin. IV. The conformers contributing to the conformation equilibrium of somatostatin in aqueous solution as found by semi-empirical energy calculations and high-resolution NMR experiments.

The results of a conformational study by 1H and 13C high-resolution NMR at 270 and 500 MHz on the peptide hormone somatostatin have been compared with a series of conformers generated by semi-empirical energy calculations. The use of specifically deuterated phenylalanine residues has enabled us to confirm and supplement the identification of all but the phenylalanine aromatic resonances in the proton spectra of somatostatin. In order to minimize the risk of overlooking some low-energy conformations, four different strategies have been used for the generation of the conformers: two based on combinations of conformations of fragments that had been studied before, one on a random procedure and one on the conformational constraints existing in bicyclic analogs with high biological activity. The experimental values of 3JNH-C alpha H and 3J alpha beta coupling constants and the existence of several ring current shifts allowed us to select from the calculations those families of low-energy conformers that are compatible with the NMR results. The NH temperature coefficients do not warrant the existence of any stable beta or gamma turns in the molecule, although the region SRIF8-12 seems to be the most stable in this respect. In addition there are several upfield shifts: 0.2-0.4 ppm on the Lys9 side-chain, 0.3-0.5 ppm on the Phe6 alpha, beta and Phe7 alpha protons, as well as some 0.2-0.3 ppm shifts on parts of two phenylalanine ring systems. Almost all of these shifts decrease considerably with increasing temperature. Most of the observed NMR results are compatible with the properties of one family of low-energy conformations whose main features are a double beta II bend Trp8-Lys9, Thr10 -Phe11, a close proximity of the Trp8 and Lys9 side chains and an orientation of Phe7 towards the Phe6 alpha, beta protons. We conclude that this set of conformations forms a major contribution to the conformational equilibrium at room temperature. The properties of this and several other sets of low-energy conformations that do not dominate in aqueous solution are discussed in relation to al available experimental evidence.

Magnetic Resonance Spectroscopy↗
PubMed1982

Structure-activity relationships of the B fragment of diphtheria toxin: the lipid-binding domains.

Two different lipid-associating domains have previously been identified in diphtheria toxin fragment B: one of the surface type in the N-terminus of B and one of the transverse type in its middle region. We have now determined about 85% of the primary structure of fragment B and show, here, that the middle part of fragment B contains a highly hydrophobic region of 72 amino acid residues (polarity index: 295) which includes the transverse lipid-associating domain. That this domain is actually involved in a process of membrane penetration is suggested by lipid bilayer conductance measurements of the CNBr peptides of fragment B and trypsin treatment of fragment B-multilamellar liposome complexes.

Amino Acid Sequence↗
PubMed1980

Primary structure of diphtheria toxin fragment B: structural similarities with lipid-binding domains.

Two different lipid-associating domains have been identified in the B fragment of diphtheria toxin using automated Edman degradation of its cyanogen bromide peptides, secondary structure prediction analysis, and comparisons with known phospholipid-interacting proteins. The first domain is located in the highly hydrophilic (polarity index [PI] = 61.0%) 9.00-dalton N-terminal region of fragment B. This region shows primary and predicted secondary structures dramatically similar to those found for the phospholipid headgroup-binding domains of human apolipoprotein A1 (surface lipid-associating domain). The second domain is located in the highly hydrophobic (PI = 32.4%) middle region of fragment B. Its structure resembles that found for the membranous domain of intrinsic membrane proteins (transverse lipid-associating domain). In contrast, the hydrophilic C-terminal 8,000-dalton region of fragment B (PI = 53.8%) does not show structural similarity with lipid-associating domains.

Amino Acid Sequence↗
PubMed1977

Diphtheria toxin: the effect of nitration and reductive methylation on enzymatic activity and toxicity.

Diphtheria toxin is rapidly inactivated upon reaction with tetranitromethane. inactivation is partially prevented in the presence of the substrate NAD. The loss of enzymatic activity and of toxicity is concomitant with the modification of one tyrosyl residue per molecule, located in the fragment A. Completely inactivated toxin (more than 5 nitrotyrosines per molecule) is a good toxin antagonist for HeLa cells binding sites indicating that the integrity of its fragment B is preserved. Methylation of lysyl residues leads to a decrease of toxicity and enzymatic activity but only after the modification of about 20 lysines per molecule. This methylated toxin however can still bind NAD and seems to possess a functional fragment B. Enzymatic site of diphtheria toxin fragment A seems thus to contain one essential tyrosyl residue implicated in the binding of NAD and at least one lysine not implicated in this dinucleotide binding.

Binding Sites↗