Solutes from extreme bacteria protect protein-coated devices from drying

A wide variety of biomedical applications require the coating of devices with immobilized proteins, ranging from functional protein microarrays and biosensors to modifying implants for better host acceptance. When exposed to air, the coatings dry, contorting proteins’ shape and diminishing a coating’s effect. New work with compounds derived from bacteria that normally live in the world’s harshest environments has given a new direction to this technology.

An international team of researchers demonstrated a new technique that stabilizes protein coatings, stopping them from changing their behavior when they are dried. Publishing their work in the journal Biointerphases, by turning to solutes that bacteria produce to retain protein functionality under extreme conditions — ectoine and hydroxyectoine — the group produced a coating that preserved dried protein monolayers for more than a day and gave a threefold increase in protein activity compared with noncoated samples.

As protein coatings dry, proteins fold so that their water-avoiding hydrophobic domains are exposed facing the air, leaving the proteins’ structure and function altered. The solutes protect the proteins by keeping them hydrated. When applied to a protein coat on titanium oxide as used for bone screws, the solutes trap a layer of water between the proteins and outside air. Time-of-flight secondary ion mass spectrometry combined with principle component analysis confirmed the proteins’ retained structure.

In colorimetric assays measuring the activity of horseradish peroxidase, use of ectoine and hydroxyectoine yielded a significantly higher protein activity for longer-term storage compared to approaches using sugar solutes.The authors said they hope the new protein coating technique will stoke further interest in using the unique properties of so-called extremophilic bacteria and that their findings will one day allow researchers to store protein-based assays for longer periods of time.

Source: “Stabilization of dry protein coatings with compatible solutes,” by Manuela S. Killian, Adam J. Taylor, and David G. Castner, Biointerphases (2018). The article can be accessed at https://doi.org/10.1116/1.5031189 .