Cobra cardiotoxins: membrane interactions and pharmacological potential
Natural polycationic membrane-active peptides typically lack disulfide bonds and exhibit fusion, cell-penetrating, antimicrobial activities. They are mostly unordered in solution, but adopt a helical structure, when bound to phospholipid membranes. Structurally different are cardiotoxins (or cytotoxins, СTs) from cobra venom. They are fully b-structured molecules, characterized by the three-finger fold (TFF). Affinity of CTs to lipid bilayer was shown to depend on amino acid sequence in the tips of the three loops. In the present review, CT-membrane interactions are analyzed through the prism of data on binding of the toxins to phospholipid liposomes and detergent micelles, as well as their structural and computational studies in membrane mimicking environments. We assess different hydrophobicity scales to compare membrane partitioning of various CTs and their membrane effects. A comparison of hydrophobic/hydrophilic properties of CTs and linear polycationic peptides provides a key to their biological activity and reveal rationality for design of new membrane-interacting compounds. Finally, since the viewpoint of the data obtained on model lipid membranes, cytotoxic activity of CTs against cancer cells is discussed.
To gain success in the evolutionary “arms race”, venomous animals such as scorpions produce diverse neurotoxins selected to hit targets in the nervous system of prey. Scorpion α-toxins affect insect and/or mammalian voltage-gated sodium channels (Nav’s) and thereby modify the excitability of muscle and nerve cells. Although more than a hundred α-toxins are known and a number of them have been studied into detail, the molecular mechanism of their interaction with Nav’s is still poorly understood. Here, we employ extensive molecular dynamics simulations and spatial mapping of hydrophobic/hydrophilic properties distributed over the molecular surface of α-toxins. It is revealed that in spite of the small size and relatively rigid structure, these toxins possess modular organization from structural, functional and evolutionary perspectives. The more conserved and rigid “core module” is supplemented with the “specificity module” (SM) that is comparatively flexible and variable, and determines the taxon (mammal vs. insect) specificity of α-toxin activity. We further show that SMs in mammal toxins are more flexible and hydrophilic than in insect toxins. Concomitant sequence-based analysis of Nav’s extracellular loops suggests that α-toxins recognize the channels using both modules. We propose that the core module binds to the voltage-sensing domain of repeat IV, whereas the more versatile SM interacts with the pore domain in repeat I of Nav’s. These findings corroborate and expand the hypothesis on different functional epitopes of toxins that has been reported previously. In effect, we propose that the modular structure in toxins evolved to match the domain architecture of Nav’s.
Mutations in transmembrane (TM) domains of receptor tyrosine kinases are shown to cause a number of inherited diseases and cancer development. Here, we use a combined molecular modeling approach to understand molecular mechanism of effect of G370R and A391E mutations on dimerization of TM domains of human fibroblast growth factor receptor 3 (FGFR3). According to results of Monte-Carlo conformational search in the implicit membrane and further molecular dynamics simulations, TM dimer of this receptor is able to form a number of various conformations, which differ significantly by the free energy of association in a full-atom model bilayer. The aforementioned mutations affect dimerization efficiency of TM segments and lead to repopulation of conformational ensemble for the dimer. Particularly, both mutations do not change the dimerization free energy of the predominant (putative “non-active”) symmetric conformation of TM dimer, while affect dimerization efficiency of its asymmetric (“intermediate”) and alternative symmetric (putative “active”) models. Results of our simulations provide novel atomistic prospective of the role of G370 and A391E mutations in dimerization of TM domains of FGFR3 and their consecutive contributions to the activation pathway of the receptor.
Ribosomal protein S2 is an essential component of translation machinery, and its viable mutated variants conferring distinct phenotypes serve as a valuable tool in studying the role of S2 in translation regulation. One of a few available rpsB mutants, rpsB1, shows thermosensitivity and ensures enhanced expression of leaderless mRNAs. In this study, we identified the nature of the rpsB1 mutation. Sequencing of the rpsB1 allele revealed a G-to-A transition in the part of the rpsB gene which encodes a coiled-coil domain of S2. The resulting E132K substitution resides in a highly conserved site, TKKE, a so-called N-terminal capping box, at the beginning of the second alpha helix. The protruding coiled-coil domain of S2 is known to provide binding with 16S rRNA in the head of the 30S subunit and, in addition, to interact with a key mRNA binding protein, S1. Molecular dynamics simulations revealed a detrimental impact of the E132K mutation on the coiled-coil structure and thereby on the interactions between S2 and 16S rRNA, providing a clue for the thermosensitivity of the rpsB1 mutant. Using a strain producing a leaderless lacZ transcript from the chromosomal lac promoter, we demonstrated that not only the rpsB1 mutation generating S2/S1-deficient ribosomes but also the rpsA::IS10 mutation leading to partial deficiency in S1 alone increased translation efficiency of the leaderless mRNA by about 10-fold. Moderate overexpression of S1 relieved all these effects and, moreover, suppressed the thermosensitive phenotype of rpsB1, indicating the role of S1 as an extragenic suppressor of the E132K mutation.