Nanoyeast and Other Cell Envelope Compositions for Protein Studies and Biosensor Applications

Rapid progress in disease biomarker discovery has increased the need for robust detection technologies. In the past several years, the designs of many immunoaffinity reagents have focused on lowering costs and improving specificity while also promoting stability. Antibody fragments (scFvs) have long been displayed on the surface of yeast and phage libraries for selection; however, the stable production of such fragments presents challenges that hamper their widespread use in diagnostics. Membrane and cell wall proteins similarly suffer from stability problems when solubilized from their native environment. Recently, cell envelope compositions that maintain membrane proteins in native or native-like lipid environment to improve their stability have been developed. This cell envelope composition approach has now been adapted toward stabilizing antibody fragments by retaining their native cell wall environment. A new class of immunoaffinity reagents has been developed that maintains antibody fragment attachment to yeast cell wall. Herein, we review recent strategies that incorporate cell wall fragments with functional scFvs, which are designed for easy production while maintaining specificity and stability when in use with simple detection platforms. These cell wall based antibody fragments are globular in structure, and heterogeneous in size, with fragments ranging from tens to hundreds of nanometers in size. These fragments appear to retain activity once immobilized onto biosensor surfaces for the specific and sensitive detection of pathogen antigens. They can be quickly and economically generated from a yeast display library and stored lyophilized, at room temperature, for up to a year with little effect on stability. This new format of scFvs provides stability, in a simple and low-cost manner toward the use of scFvs in biosensor applications. The production and "panning" of such antibody cell wall composites are also extremely facile, enabling the rapid adoption of stable and inexpensive affinity reagents for emerging infectious threats.