Abstract Background Insects can be found in numerous diverse environments, being exposed to pathogenic organisms like fungi and bacteria. Once these pathogens cross insect physical barriers, the innate immune system operates through cellular and humoral responses. Antimicrobial peptides are small molecules produced by immune signaling cascades that develop an important and generalist role in insect defenses against a variety of microorganisms. In the present work, a cecropin B-like peptide (AgCecropB) sequence was identified in the velvetbean caterpillar Anticarsia gemmatalis and cloned in a bacterial plasmid vector for further heterologous expression and antimicrobial tests. Methods AgCecropB sequence (without the signal peptide) was cloned in the plasmid vector pET-M30-MBP and expressed in the Escherichia coli BL21(DE3) expression host. Expression was induced with IPTG and a recombinant peptide was purified using two affinity chromatography steps with Histrap column. The purified peptide was submitted to high-resolution mass spectrometry (HRMS) and structural analyses. Antimicrobial tests were performed using gram-positive (Bacillus thuringiensis) and gram-negative (Burkholderia kururiensis and E. coli) bacteria. Results AgCecropB was expressed in E. coli BL21 (DE3) at 28°C with IPTG 0.5 mM. The recombinant peptide was purified and enriched after purification steps. HRMS confirmed AgCrecropB molecular mass (4.6 kDa) and circular dichroism assay showed α-helix structure in the presence of SDS. AgCrecropB inhibited almost 50% of gram-positive B. thuringiensis bacteria growth. Conclusions The first cecropin B-like peptide was described in A. gemmatalis and a recombinant peptide was expressed using a bacterial platform. Data confirmed tertiary structure as predicted for the cecropin peptide family. AgCecropB was capable to inhibit B. thuringiensis growth in vitro.

Bactérias são capazes de sincronizar seu comportamento populacional a fim de regular a expressão gênica por meio de um mecanismo de comunicação célula-a-célula denominado quorum sensing. Este fenômeno envolve a produção, detecção e resposta a moléculas sinalizadoras extracelulares chamadas de auto-indutores, que direta ou indiretamente regulam a expressão de genes de maneira dependente da densidade celular. Quorum sensing controla uma grande variedade de processos biológicos em bactérias, tais como bioluminescência, produção de fatores de virulência, formação de biofilme e resistência a antibiótico. Os auto-indutores são reconhecidos por receptores específicos, que podem ser tanto receptores histidina quinases associados a membranas, que funcionam através da ativação de reguladores de resposta citoplasmáticos cognatos, quanto receptores citoplasmáticos que atuam como fatores de transcrição. Nesta revisão, nós focamos nos reguladores de quorum sensing citosólicos, cujas estruturas tridimensionais auxiliaram na elucidação dos seus mecanismos de ação. Estudos estruturais de receptores de quorum sensing podem viabilizar o desenho racional de moléculas inibitórias. Finalmente, esta abordagem pode representar uma alternativa eficaz no tratamento de infecções onde a terapia antimicrobiana clássica é incapaz de superar a virulência do micro-organismo.

Bacteria are able to synchronize the population behavior in order to regulate gene expression through a cell-to-cell communication mechanism called quorum sensing. This phenomenon involves the production, detection and the response to extracellular signaling molecules named autoinducers, which directly or indirectly regulate gene expression in a cell density-dependent manner. Quorum sensing may control a wide range of biological processes in bacteria, such as bioluminescence, virulence factor production, biofilm formation and antibiotic resistance. The autoinducers are recognized by specific receptors that can either be membrane-bound histidine kinase receptors, which work by activating cognate cytoplasmic response regulators, or cytoplasmic receptors acting as transcription factors. In this review, we focused on the cytosolic quorum sensing regulators whose three-dimensional structures helped elucidate their mechanisms of action. Structural studies of quorum sensing receptors may enable the rational design of inhibitor molecules. Ultimately, this approach may represent an effective alternative to treat infections where classical antimicrobial therapy fails to overcome the microorganism virulence.