Two proline-rich peptides from pig (Sus scrofa) salivary glands generated by pre-secretory pathway underlying the action of a proteinase cleaving ProAla bonds.

The primary structures of two salivary proline-rich peptides (PRP-SP-A, M 6156.0 amu and PRP-SP-B, M 1905.0 amu), from pig (Sus scrofa) were determined. The PRP-SP-B peptide, 21 residues long, overlaps with a sequence repeated 43 times in three deposited cDNAs coding for PRP proteins cloned from porcine parotid glands (Swiss-Prot codes: Q95JC9, Q95JD1, Q95JD0). PRP-SP-A peptide, 56 amino acid residues long, overlaps with the N-terminus repeats of Q95JC9 and Q95JD1 and it is phosphorylated at Ser 12 and 14. The two peptides were found both in whole saliva and in granules from pig parotid glands. The biosynthesis of the two peptides implies the action of a proteinase responsible for Pro downward arrow Ala cleavage in the pre-secretory process.

Human salivary peptides derived from histatins.

Human saliva from a healthy donor was subjected to fractionation by gel chromatography and six pools were collected and analysed by MALDI-TOF-MS and HPLC-ESI-MS. Three peptides, corresponding to 888.3, 687.3, and 524.1 amu and SNYLYDN, YLYDN, and LYDN sequences (determined by automated Edman sequencing), were isolated from pool 4. YLYDN was not previously described in human saliva. The peptides show the common C-terminal sequence of histatin 3 and histatin 1. To exclude the possibility that the three peptides were an artifact of the purification procedure, nine samples of human saliva were collected from healthy donors, immediately acidified with 0.2% TFA, and analysed by RP-HPLC-ESI-MS. The three peptides were detected in all the analyzed samples. SNYLYDN was always found at a concentration higher than that of YLYDN and LYDN. A correlation analysis performed on quantitative data indicated that the three peptides derive only from histatin 3. Other already known histatins also were searched for in the chromatogram. Histatins 1, 2, 3, 5, 6, 7, 8, and 10 were observed, although not in all samples analyzed, whereas other minor histatins were not detected.

Inhibition of AChE: structure-activity relationship among conformational transition of Trp84 and biomolecular rate constant.

In this study the authors attempt to correlate kinetic constants for carbamylation of AChE, by a series of carbamate inhibitors, with the conformational positioning of Trp84 in transition state complexes of the same carbamates with Torpedo AChE, as obtained by computerized molecular modelling. They present evidence for changes in the distance of the carbamates from the center of the indole ring which can be correlated with the bimolecular rate constants for inhibition. As a result the greater the distance from Trp84, the smaller the bimolecular inhibition constant value, ki (= k2/Ka), becomes. In conclusion, the value of the bimolecular rate constant for selected AChE inhibitors (structural changes that have been hypothesised or natural alkaloids of unknown activity) which possess similar size and rigidity, can be obtained. Under these conditions energy minimization alone seems to be sufficient even to accurately predict protein-substrate interactions that actually occur. Modelling studies also suggest that conformational re-orientation of Trp84 in the transition state could produce an overall movement of the Cys67-Cys94 loop.

Anionic binding site and 2,3-DPG effect in bovine hemoglobin.

It is generally believed that bovine hemoglobin (BvHb) interacts weakly with 2,3-diphosphoglycerate (2,3-DPG) in a chloride-free media and not at all in the presence of physiological concentrations of chloride (100 mM). This lack of interaction has raised several questions at both structural and evolutionary levels. Results obtained in this study via 31P nuclear magnetic resonance (NMR) show that, even in the presence of 100 mM chloride ions, 2,3-DPG does, in fact, interact with bovine deoxy-Hb. This spectroscopic observation has been confirmed by oxygen binding experiments, which have also shown that, under certain conditions, chloride and 2,3-DPG may display a synergistic effect in modifying the oxygen affinity of bovine hemoglobin. It could be that this synergistic effect has its structural basis in a conformational modification induced by 2,3-DPG, possibly causing extra chloride anions to approach the positive charges which constitute the anion binding site. Another possibility, not necessarily an alternative, is the additional chloride binding site recently identified [Fronticelli, C., Sanna, M. T., Perez-Alvarado, G. C., Karavitis, M., Lu, A.-L., and Brinnigar, W. S. (1995) J. Biol. Chem 270, 30588-30592] involving lysine beta76 that in bovine Hb substitutes for the alanine residue present in human hemoglobin. All of these findings are in agreement with the very low enthalpy of oxygenation that characterizes bovine Hb when both chloride and 2,3-DPG are present in concomitance. The results reported here clearly show that bovine hemoglobin does react with 2, 3-DPG and is functionally affected by this organic phosphate. Hence, the very low intraerythrocytic concentration of 2,3-DPG (0.5 mM) in adult bovine red blood cells is the result of metabolic adaptation which cannot be explained solely by the different amino acid sequence at the level of the 2,3-DPG binding site.

The role of TRP84 in catalytic power and the specificity of AChE.

The structure-function relationship between the alkaloids physostigmine, physovenine and the three structurally related compounds were investigated by employing kinetic studies and molecular modeling. Crystallographic data from the X-ray conformation of the Torpedo californica acetylcholinesterase complex together with the transition state analog inhibitor m-(N,N,N,-Trimethylammonio) trifluoroacetophenone (TMTFA) was used as template onto which inhibitors were superimposed. Among the structural elements of the active site, TRP84 residue shows a versatile role. In fact, its aromatic electrons not only can be employed in pi-cation interactions, as is the case for ACh, but they can also provide a polarizable surface for van der Waals and London interactions.

Studies on a new series of THA analogues: effects of the aromatic residues that line the gorge of AChE.

A series of N-monoalkylsubstituted 1,2,3,4-tetrahydro-9-aminoacridines have been prepared after modelling simulation of the AChE-inhibitor complex. Molecular modelling has predicted a number of hydrophobic residues to be involved in the catalytic mechanism of this interaction between the binding sites of AChE and this series of aminoacridines. In these compounds the acridine moiety becomes sandwiched between the rings of PHE330 and TRP84. In particular, the alkyl chain shows the important role of aromatic groups as binding sites. Their in vitro inhibitory properties (enzyme from Electrophorus electricus) confirm the aromatic groups as a general and significant characteristic of the mechanism of AChE inhibition.

Bovine hemoglobin cross-linked through the beta chains: functional and structural aspects.

2-Nor-2-formylpyridoxal (NFPLP) has been synthesized and coupled to bovine Hb according to the procedure developed by Benesch and Benesch. The reaction of bovine Hb with NFPLP leads to a cross-linkage between the beta subunits, which greatly stabilizes the low affinity T state of the molecule and simultaneously abolishes the tendency of the tetramer to dissociate into alpha beta dimers. The functional properties, examined from both the equilibrium and kinetic points of view, indicate that the chemical modification affects the O2 affinity, abolishes cooperativity, and induces a slight decrease of the Bohr effect. From modeling studies we are confronted with two different structural alternatives; the cross-link of beta chains may be formed between lysine 82 of beta2 and the N terminus of methionine 2 of beta1 or between the two lysine 82 residues of both beta2 chains. Digestion of modified beta globin chains and isolation of the cross-linked peptide have showed that NFPLP cross-links Met-beta2 and Lys-beta82. This allowed discussion in some detail of the molecular basis of the Bohr effect of the modified bovine hemoglobin. On the whole, NFPLP-modified bovine Hb could be considered as a first step toward the synthesis of a potential blood substitute.

On the alkaloids of Strychnos. XXXV. The occurrence of akagerine in South American Strychnos.

Akagerine (3) was isolated from three different species of South American Strychnos: from S. gardneri A. D.C. (Rio de Janeiro, Brazil), together with 11-methoxydiaboline (2); from S. jobertiana Baillon (Brazil), together with diaboline (1): and from S. parvifolia D.C. (Bahia, Brazil).