Synthesis, Structure, and Properties of MeSer¹-Tentoxin, a New Cyclic Tetrapeptide Which Interacts Specifically with Chloroplast F₁H⁺-ATPase Differentiation of Inhibitory and Stimulating Effects

Abstract

A new tentoxin analogue, in which the L-methyl alanine residue is substituted by L-methylserine, has been prepared following the synthetic pathway recently described for the synthesis of tentoxin [Cavelier, F., & Verducci, J. (1995) Tetrahedron Lett. 36, 4425-4428]. Using two-dimensional homonuclear proton nuclear magnetic resonance and structural analysis, we observed that MeSer1-tentoxin, like tentoxin, adopts several conformations in aqueous solution and presents self-aggregative properties. This analogue was found to be conformationally similar to the natural toxin. It showed the same efficiency as tentoxin in inhibition of ATPase activity of the isolated chloroplast F1 proton ATPase (CF1) as well as in inhibition of the ATP synthase activity of the membrane-bound enzyme (CF0CF1) in thylakoids and proteoliposomes. At concentrations above 10 microM, MeSer1-tentoxin did not reactivate CF1 to a high extent, contrary to tentoxin. It appeared, however, to bind in the same way, since the reactivating effect of tentoxin was inhibited by MeSer1-tentoxin. These results show that it is possible, using tentoxin analogues, to separate inhibitory and activating effects on the chloroplast ATPase, despite the limited chemical difference between the two toxins.

Structure of spinach chloroplast F 1 -ATPase complexed with the phytopathogenic inhibitor tentoxin

“…The two major forms differ in the position of the peptide bond formed between MeAla-1 and Leu-2, which is f lipped in the B-conformer. A shift in the equilibrium of the A-and B-conformers was reported for the MeSer-1 derivate of tentoxin, where, because of an intramolecular hydrogen bond, the B-conformer becomes the predominant form in aqueous solution (20). The crystallographic data of our inhibitor complex suggest that the B-conformer is the bound species in the tentoxin-inhibited chloroplast F 1 -ATPase.…”

“…For calculation of the R free -value (18), 5% of the observed reflections were set aside and excluded from the entire refinement, including the initial rigid-body minimization. Tentoxin was built into a A weighted-difference density map with the graphics program O (19) using structural information of MeSer-1-Tentoxin obtained by NMR-spectroscopy, restrained molecular dynamics simulations (20), and…”

ATP Synthase and the Actions of Inhibitors Utilized To Study Its Roles in Human Health, Disease, and Other Scientific Areas

“…For example, tentoxin is a strong inhibitor of CF 1 -ATPase from certain sensitive species such as spinach, potato, and lettuce, but it has little or no inhibitory effect on the same enzyme from insensitive species such as corn, tobacco, and radish, even though they exhibit high sequence and structural similarity (380). In addition, slight structural modifications of tentoxin can cause dramatic effects on the properties and inhibitory potencies of the inhibitor (316,351). Finally, the drug R207910, developed for the treatment of tuberculosis, also shows a narrow selectivity in its inhibition of the ATP synthase in mycobacterial species (15).…”

“…Here, it blocks the contact between ␣Arg-297 and ␤Asp-83 (153,155), restrains the movements of these residues, and also restrains conformational changes at the catalytic interface. This may arrest the catalytic ␣␤ interface in the closed conformation and thereby hinder its transformation into the open conformation (153,155 (316,351) (Fig. 2C).…”

Natural Compounds as Next-Generation Herbicides

“…2). Tentoxin, a cyclic tetrapeptide from the plant pathogen A. tenuis (Saad et al, 1970), inhibits chloroplast development , interacting directly with chloroplast CF1 ATPase (Pinet et al, 1996;Groth, 2002;Meiss et al, 2008). This compound acts like a selective herbicide (Durbin and Uchytil, 1977;Lax et al, 1988) and has been the focus of a combinatorial synthesis program based on its unique structural scaffold (Jiménez et al, 2003).…”