A Thymic Metallo-Peptide Influences Lymphocyte, Monocyte and Thymocyte Responses

Torres-Aguilar Lorena Osuna-Martínez Ulises

doi:10.4172/2161-0398.1000119

Abstract

Non-covalent metal-peptide interactions are critical in peptide assembly, folding, stability, and function. Zinc has chemical, structural and regulatory functions in biological systems. The present study investigated the changes caused by the addition of Zn2+ on the biological activity of a thymic peptide on immune cells. For this purpose, we exposed different cells to 10-10 M peptide and different concentrations of Zn2+, Mg2+ and Cu2+ for 24 and 48 h, and monitored the proliferative and phagocytic activities of the treated cells. We also performed NMR and chromatography analysis of the peptide in the presence of Zn2+ and other ions. Peptide activity increased in the presence of Zn2+, Mg2+ or Cu2+, and this increase was over 100-fold in the presence of Zn2+. NMR studies indicated that the peptide exhibited field displacements: Glutamic acid (D) to low-field NMR (Δδ+0.027 ppm), and both aspartic acid (E) and the leucine with a terminal carboxylic acid (L8) to high-field NMR (Δδ-0.016 and -0.051 ppm, respectively). In addition, the retention time in HPLC decreased in the presence of ions. Our findings show that the peptide loses its biological activity in the presence of a zinc-chelating agent. That is, the presence of zinc and other metals to a lesser extent is essential for the activity of the peptide. This unexpected dependence on zinc appears to be due to the active form of the peptide-zinc complex, for which we propose the name of “immuno-modulator metallo-peptide” (IMMP).

Highlights

Metal-ligand interactions are critical components of the metallopeptide assembly, folding, stability, electrochemistry, and function
Phytohemagglutinin (PHA), Concanavalin A (ConA), Diethylenetriaminepentaacetic acid (DTPA), Dimethyl sulfoxide (DMSO), as well as the Ficoll-Hypaque and Ficoll-Paque Plus gradients were from Sigma-Aldrich Co
Due to the length of the peptide it was not expected to present secondary structure; circular dichroism (CD) experiments showed a typical spectrum of a random coil chain that is not affected by the presence of Zn2+ (Figure 1)

Summary

Introduction

Metal-ligand interactions are critical components of the metallopeptide assembly, folding, stability, electrochemistry, and function. Experimental zinc deprivation leads to generalized lymphoid hypoplasia, rapid thymic involution ( of the cortex), and decreased production of thymic hormones, impaired lymphocyte proliferative capacity after phytomitogen stimulation, and reduced antibody and cell-mediated responses [1,2,3,4]. Polypeptides and basic proteins have all been proposed to be natural mitotic stimulants, both in vivo and in vitro, serving to initiate cell division [5,6,7,8]. The thymic octapeptide Leu-Glu-Asp-Gly-Pro-LysPhe-Leu (L1EDGPKFL8) has been implicated in augmenting T-cell functions, such as the response to T-cell lectins and mixed lymphocyte reactions; it increases interleukin-2 production by T-cells [9]. We, investigated whether any metal could modify the activity of the peptide or not

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