RESUMO
Three-finger toxins (TFTs) are well-recognized non-enzymatic venom proteins found in snakes. However, although TFTs exhibit accelerated evolution, the drivers of this evolution remain poorly understood. The structural complexes between long-chain α-neurotoxins, a subfamily of TFTs, and their nicotinic acetylcholine receptor targets have been determined in previous research, providing an opportunity to address such questions. In the current study, we observed several previously identified positively selected sites (PSSs) and the highly variable C-terminal loop of these toxins at the toxin/receptor interface. Of interest, analysis of the molecular adaptation of the toxin-recognition regions in the corresponding receptors provided no statistical evidence for positive selection. However, these regions accumulated abundant amino acid variations in the receptors from the prey of snakes, suggesting that accelerated substitution of TFTs could be a consequence of adaptation to these variations. To the best of our knowledge, this atypical evolution, initially discovered in scorpions, is reported in snake toxins for the first time and may be applicable for the evolution of toxins from other venomous animals.
Assuntos
Venenos de Serpentes/genética , Animais , Evolução Molecular , Variação Genética/genética , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismo , Receptores Nicotínicos/genética , Receptores Nicotínicos/metabolismo , Venenos de Serpentes/metabolismo , Serpentes/genéticaRESUMO
There are at least three conserved protein folds shared by ion channel-targeted neurotoxins and antimicrobial defensins, including cysteine-stabilized α-helix and ß-sheet fold (CSαß), inhibitor cystine knot fold (ICK) and ß-defensin fold (BDF). Based on a combined data of sequences, structures and functions, it has been proposed that these neurotoxins could originate from related ancient antimicrobial defensins by neofunctionalization. This provides an ideal system to study how a novel function emerged from a conserved structural scaffold during evolution. The elucidation of functional novelty of proteins not only has great significance in evolutionary biology but also will be helpful in guiding rational molecular design. This review describes recent progresses in origin of neurotoxins, focusing on the three conserved protein scaffolds.
Assuntos
Defensinas/química , Neurotoxinas/química , Evolução Molecular , Estrutura Secundária de ProteínaRESUMO
The gamma-KTx-type scorpion toxins specific for K+ channels were found to interact with ERG channels on the turret region, while alpha-KTx3.2 Agitoxin-2 binds to the pore region of the Shaker K+ channel, and alpha-KTx5.3 BmP05 binds to the intermediate region of the small-conductance calcium-activated K-channel (SK(Ca)). In order to explore the critical residues for gamma-KTx binding, we determined the NMR structure of native gamma-KTx1.1 (CnErg1), a 42 amino acid residues scorpion toxin isolated from the venom of the Mexican scorpion Centruroïdes noxius Hoffmann, and we used computational evolutionary trace (ET) analysis to predict possible structural and functional features of interacting surfaces. The 1H-NMR three-dimensional solution structure of native ergtoxin (CnErg1) was solved using a total of 452 distance constraints, 13 3J(NH-Halpha) and 10 hydrogen bonds. The structure is characterized by 2 segments of alpha-helices and a triple-stranded antiparallel beta-sheet stabilized by 4 disulfide bridges. The ET and structural analysis provided indication of the presence of two important amino acid residue clusters, one hydrophobic and the other hydrophilic, that should be involved in the surface contact between the toxin and the channel. Some features of the proposed interacting surface are discussed.
Assuntos
Bloqueadores dos Canais de Potássio/química , Canais de Potássio de Abertura Dependente da Tensão da Membrana , Canais de Potássio/química , Venenos de Escorpião/química , Sequência de Aminoácidos , Animais , Sequência Consenso , Canal de Potássio ERG1 , Canais de Potássio Éter-A-Go-Go , Evolução Molecular , Humanos , Ligação de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Modelos Moleculares , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Filogenia , Bloqueadores dos Canais de Potássio/metabolismo , Bloqueadores dos Canais de Potássio/farmacologia , Canais de Potássio/efeitos dos fármacos , Canais de Potássio/metabolismo , Ligação Proteica , Conformação Proteica , Mapeamento de Interação de Proteínas , Venenos de Escorpião/metabolismo , Venenos de Escorpião/farmacologia , Alinhamento de Sequência , Software , Relação Estrutura-AtividadeRESUMO
The scorpion venom peptides with no disulfide bridge are rarely identified and poorly characterized so far. Here, we report the identification and characterization of four novel disulfide-bridge-free venom peptides (BmKa1, BmKa2, BmKb1 and BmKn2) from Buthus martensii Kasch. BmKa1 and BmKa2 are very acidic and hydrophilic, showing no any similarity to other proteins, whereas BmKb1 and BmKn2 both are basic, alpha-helical peptide with an amidated C-terminus, showing a little homology with other peptides. Functional tests with synthetic peptide showed that BmKn2 has strong antimicrobial activity against both Gram-positive and Gram-negative bacteria, whereas BmKb1 has weak activity in inhibiting the growth of these bacteria.
