Biophysical characterization of the zinc-binding protein AdcA from Enterococcus faecium- Best Poster Award, sponsored by Wiley-VCH

The increasing spread of antimicrobial resistance in Enterococcus faecium, one of the most problematic nosocomial pathogens, poses a pressing challenge to public health due to its remarkable adaptability and the limited effectiveness of available therapeutic options . To address this issue, it is essential to identify new molecular targets involved in vital bacterial processes. Among these, nutrient acquisition systems have emerged as promising candidates, as they play a central role in bacterial survival and virulence.Zinc is an essential trace element required for numerous cellular functions. During infection, however, the host deliberately restricts its availability through a defense mechanism known as “nutritional immunity.” In response, many bacteria have evolved high-affinity zinc transport systems that enable them to overcome metal limitation and maintain intracellular homeostasis .In Gram-positive bacteria, the AdcABC transporter is one of the main systems responsible for zinc uptake and is crucial for bacterial growth under zinc-restricted conditions . In E. faecium, the AdcA protein acts as the zinc-binding component of this complex and is considered essential for survival in metal-depleted environments. Bioinformatic analyses revealed that AdcA consists of two functional domains: an N-terminal ZnuA-like domain and a C-terminal ZinT domain, connected by a flexible linker. Both domains contain histidine residues likely involved in zinc coordination. A three-dimensional model, generated by homology with the corresponding protein from Streptococcus pneumoniae, showed a high degree of structural similarity between the two species.To characterize AdcA, the protein was recombinantly expressed in Escherichia Coli, purified, and subjected to biophysical analyses. Circular dichroism (CD) spectroscopy was used to assess its secondary structure content, differential scanning calorimetry (DSC) provided insights into thermal stability, and isothermal titration calorimetry (ITC) allowed quantification of zinc-binding affinity under controlled conditions.Overall, the data suggest that AdcA plays a key role in the zinc acquisition mechanism of E. faecium, underlining its importance for bacterial survival in zinc-limited environments. Since zinc availability is significantly reduced during infection, interference with AdcA function could weaken the pathogen, offering a potential route for the development of novel antimicrobial strategies targeting metal ion homeostasis.Although further studies are required to validate its therapeutic potential, this work may provide a valuable foundation for future research aimed at disrupting nutrient acquisition pathways in multidrug-resistant pathogens. By targeting essential metal uptake systems such as AdcA, it may be possible to impair the persistence and virulence of E. faecium, contributing to innovative approaches against infections caused by antibiotic-resistant bacteria.