Molecular basis of angiotensin- and thrombin-induced endothelium-independent vasoconstriction and proliferation

Summary In this report we describe our own attempt to explain the similarity of some effects of unique endogenous bioregulators such as angiotensin and thrombin at the molecular level. We also briefly review the cellular effects and signalling pathways of these molecules. Recent studies indicate that thrombin displays two opposing vascular effects: endothelium-dependent relaxation and endothelium-independent vasoconstriction. However, it should be noted that this enzyme possesses both vasocontractile and growth-stimulating activities which are similar to those of angiotensin. To examine a molecular basis for the functional duality of thrombin and similarity with angiotensin-induced effects, we analyzed the thrombin sequence and 3D structure. We found that (i) segment 84–135 of thrombin includes two angiotensin-like sites, which contain the repeats of the Tyr-Ile-His-Pro sequence and are identical to the functionally important fragment of angiotensin; and (ii) the thrombin 68–150 domain resembles the C-terminal tail of the macrophage migration inhibitory factor (MIF): five of the eight residues in angiotensin (Asp-Arg-Val-Tyr-Ile) are identical to fragment 94–98 of this one. Thus, angiotensin shares a surprisingly high degree of structural homology with both these molecules. We anticipated that angiotensin-like sites of thrombin (fragments 86–95 and 117–127) might be responsible for its vascular and growth-promoting activities on vascular smooth muscle cells. Taken together, the data obtained from a comparative analysis of thrombin, angiotensin and macrophage migration inhibitory factor-induced effects enable us to reveal the regulatory responsible domain of the enzyme and may prove useful for drug design.     

Chemoselective biotransformation of nitriles by Rhodococcus equi A4

Resting cells of Rhodococcus equi A4 (free or immobilized in hydrogels) produced monomethyl isophtalate 1c and monomethyl terephtalate 2c from methyl-3-cyanobenzoate 1a and methyl-4-cyanobenzoate 2a, respectively, via the intermediate carboxamides 1b and 2b. The use of dried immobilized biocatalysts resulted in an increased formation of the unwanted cyano acids 1d and 2d. © Rapid Science Ltd. 1998     

Functional Reconstitution of a Prokaryotic K+ Channel

SliK, a K⁺ channel encoded by the Streptomyces KcsA gene, was expressed, purified, and reconstituted in liposomes. A concentrative ⁸⁶Rb⁺ flux assay was used to assess the ion transport properties of SliK. SliK-mediated ionic flux shows strong selectivity for K⁺ over Na⁺ and is inhibited by micromolar concentrations of Ba²⁺, mirroring the basic permeation characteristic of eukaryotic K⁺ channels studied by electrophysiological methods. ⁸⁶Rb⁺ uptake kinetics and equilibrium measurements also demonstrate that the purified protein is fully active.