Design, conformational studies and analysis of structure–function relationships of PTH (1–11) analogues: the essential role of Val in position 2

The N-terminal 1-34 segment of parathyroid hormone (PTH) is fully active in vitro and in vivo and it elicits all the biological responses characteristic of the native intact PTH. Recent studies reported potent helical analogues of the PTH (1-11) with helicity-enhancing substitutions. This work describes the synthesis, biological activity, and conformational studies of analogues obtained from the most active non-natural PTH (1-11) peptide H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH2; specifically, the replacement of Val in position 2 with D-Val, L-(αMe)-Val and N-isopropyl-Gly was studied. The synthesized analogues were characterized functionally by in-cell assays and their structures were determined by CD and NMR spectroscopy. To clarify the relationship between the structure and activity, the structural data were used to generate a pharmacophoric model, obtained overlapping all the analogues. This model underlines the fundamental functional role of the side chain of Val2 and, at the same time, reveals that the introduction of conformationally constrained Cα-tetrasubstituted α-amino acids in the peptides increases their helical content, but does not necessarily ensure significant biological activity.     

A basic peroxidase from wheat kernel with antifungal activity.

A basic heme-peroxidase (WP1) was purified to homogeneity from wheat (Triticum aestivum) kernels. The protein was not glycosylated and exhibited a molecular mass of 36 kDa and a pI of 8.0. The N-terminal amino acid sequence revealed a very high similarity with a wheat flour peroxidase allergen associated with baker's asthma. WPI showed indole-3-acetic acid oxidase activity in the presence of Mn2+ and phenolic cofactors. Antifungal assays performed in vitro towards phytopathogenic fungi indicated that WP1 was active in inhibiting germ tube elongation. This first report on antifungal properties of a heme-peroxidase gives experimental support to the idea that peroxidases play a defensive role against invading pathogens.     

Recombinant Wheat Antifungal PR4 Proteins Expressed in Escherichia coli

PR proteins are soluble and host-coded molecules with antifungal activity induced by a variety of agents. Wheat contains several PR proteins and among them are those of the class 4 coded wheatwin1 and wheatwin2; the two native proteins have been isolated from wheat kernel and the coding cDNA clones have been recently characterized. Herein, we report the expression of recombinant wheatwin1 and wheatwin2 in Escherichia coli-insoluble fractions; a new protocol for the purification in high yields and correct processing of the two proteins was developed. The recombinant proteins have molecular weights identical to that of the native proteins, indicating that the removal of the N-terminal methionine and cyclization of glutamine to pyroglutamate was complete. Both recombinant proteins inhibited in vitro the growth of Fusarium culmorum exhibiting antifungal properties similar to those of the native proteins.     

Structure-function relationship studies of PTH(1-11) analogues containing sterically hindered dipeptide mimetics.

The N-terminal 1-34 fragment of parathyroid hormone (PTH) is fully active in vitro and in vivo and reproduces all biological responses characteristic of the native intact PTH. In order to develop safer and non-parenteral PTH-like bone anabolic agents, we have studied the effect of introducing conformationally constrained dipeptide mimetics into the N-terminal portion of PTH in an effort to generate miniaturized PTH-mimetics. To this end, we have synthesized and conformationally and biologically characterized PTH(1-11) analogues containing 3R-carboxy-6S-amino-7,5-bicyclic thiazolidinlactam (7,5-bTL), a rigidified dipeptide mimetic unit. The wild type sequence of PTH(1-11) is H-Ser-Val-Ser-Glu-Ile-Gln-Leu-Met-His-Asn-Leu-NH(2). The following pseudo-undecapeptides were prepared: [Ala(1), 7,5-bTL(3, 4), Nle(8), Arg(11)]hPTH(1-11)NH(2) (I); [Ala(1), 7,5-bTL(6, 7), Nle(8), Arg(11)]hPTH(1-11)NH(2) (II); [Ala(1), Nle(8), 7,5-bTL(9, 10), Arg(11)]hPTH(1-11)NH(2) (III). In aqueous solution containing 20% TFE, only analogue I exhibited the typical CD pattern of the alpha-helical conformation. NMR experiments and molecular dynamics calculations located the alpha-helical stretch in the sequence Ile(5)-His(9). The dipeptide mimetic unit 7,5-bTL induces a type III beta-turn, occupying the positions i - 1 and i of the turn. Analogue II exhibited an equilibrium between a type I beta-turn and an alpha-helix, and analogue III did not show any ordered structure. Biological tests revealed poor activity for all analogues (EC(50) > 0.1 mM). Apparently, the relative side-chain orientation of Val(2), Ile(5) and Met(8) can be critical for effective analogue-receptor interaction. Considering helicity as an essential property to obtain active PTH agonists, one must decorate the correctly positioned dipeptide mimetic azabicycloalkane scaffold with substitutions corresponding to the displaced amino acids.     

Probing the modelled structure of wheatwin1 by controlled proteolysis and sequence analysis of unfractionated digestion mixtures.

We set up a method to get rapid information on the three-dimensional structure of peptide and proteins of known sequence. Both native and alkylated polypeptide is hydrolyzed with a number of proteases at different digestion times and the resulting mixtures are compared by HPLC analysis to establish the differences in the hydrolysis pathways of the folded and unfolded molecule. Then, the unfractionated digestion mixtures of the native polypeptide are submitted to automatic sequence analysis to identify the hydrolysis sites. The sequence of each fragment present in the mixtures is reconstructed and its amount determined by quantitative data of the sequence analyses. We used this approach to determine the amino acid surface accessibility of wheatwin1, a pathogenesis-related protein from wheat, and constructed a predictive three-dimensional model based on the knowledge of the tertiary structure of barwin, a highly homologous protein from barley. The procedure allowed us to quickly identify and quantify the hydrolysis at the susceptible bonds which could be classified as exposed, partially hidden, or inaccessible. The results were useful to evidentiate and discuss concordances and differences between experimental and model predicted accessibilities of amino acid residues. Proteins 1999;36:192-204.     

Role of the guanidine group in the N-terminal fragment of PTH(1–11)

A series of PTH hybrids containing a diamine [NH₂(CH₂) _n NH₂; n = 4, 5, 6] in the C-terminal position was synthesized based on the H-Aib-Val-Aib-Glu-Ile-Gln-Leu-Nle-His-Gln-Har-NH₂ (Har = homoarginine) template. The compounds were pharmacologically characterized at PTH1R receptors for agonist activity.     

An algorithm to analyse the hydrolysis pathway of peptides and proteins by sequence analyses of unfractionated digestion mixtures

We have designed and implemented on a personal computer a programfor identifying and quantifying the fragments present in a peptidemixture obtained by hydrolysing a polypeptide of known sequenceusing digesting agents. The qualitative data utilized by themain algorithm consist of the target sequence of the intactmolecule and the amino acid residues identified at each stepof the automatic sequence analysis of the unfractionated digestionmixture. In this way, the sequence of each fragment presentin the mixture is quickly reconstructed. Furthermore, if thequantitative data of the amino acid residues identified at eachstep of the sequence analysis are utilized, the program willcorrelate the sequence of each fragment to its amount. We furnishan example of the application intended for the rapid identificationand characterization of the extracellular proteinases producedby a basidiomycete fungus, utilizing the bovine insulin ß3-chainas target substrate. A variety of uses for the method are discussed.