A DsbA-Deficient Periplasm Enables Functional Display of a Protein with Redox-Sensitive Folding on M13 Phage

Preparation of Bioconjugates of Chimeric M13 Phage and Gold Nanorods

Phage-nanomaterial conjugates are functional bio-nanofibers with various applications. While phage display can select for phages with desired genetically encoded functions and properties, nanomaterials can endow the phages with additional features at nanoscale dimensions. Therefore, combining phages with nanotechnology can construct bioconjugates with unique characteristics. One strategy for filamentous phages is to adsorb nanoparticles onto the side wall, composed of pVIII subunits, through electrostatic interactions. However, a noncovalent approach may cause offloading if the environment changes, potentially causing side effects especially for in vivo applications. Therefore, building stable phage-bioconjugates is an important need. We previously reported the construction of chimeric M13 phage conjugated with gold nanorods, named "phanorods," without weakening the binding affinity to the bacterial host cells. Herein, we give a detailed protocol for preparing the chimeric M13 phage and covalently conjugating gold nanorods to the phage.

Harnessing the potential of bacterial oxidative folding to aid protein production

Protein folding is central to both biological function and recombinant protein production. In bacterial expression systems, which are easy to use and offer high protein yields, production of the protein of interest in its native fold can be hampered by the limitations of endogenous posttranslational modification systems. Disulfide bond formation, entailing the covalent linkage of proximal cysteine amino acids, is a fundamental posttranslational modification reaction that often underpins protein stability, especially in extracytoplasmic environments. When these bonds are not formed correctly, the yield and activity of the resultant protein are dramatically decreased. Although the mechanism of oxidative protein folding is well understood, unwanted or incorrect disulfide bond formation often presents a stumbling block for the expression of cysteine-containing proteins in bacteria. It is therefore important to consider the biochemistry of prokaryotic disulfide bond formation systems in the context of protein production, in order to take advantage of the full potential of such pathways in biotechnology applications. Here, we provide a critical overview of the use of bacterial oxidative folding in protein production so far, and propose a practical decision-making workflow for exploiting disulfide bond formation for the expression of any given protein of interest.

An engineered high affinity Fbs1 carbohydrate binding protein for selective capture of N-glycans and N-glycopeptides

A method for selective and comprehensive enrichment of N-linked glycopeptides was developed to facilitate detection of micro-heterogeneity of N-glycosylation. The method takes advantage of the inherent properties of Fbs1, which functions within the ubiquitin-mediated degradation system to recognize the common core pentasaccharide motif (Man3GlcNAc2) of N-linked glycoproteins. We show that Fbs1 is able to bind diverse types of N-linked glycomolecules; however, wild-type Fbs1 preferentially binds high-mannose-containing glycans. We identified Fbs1 variants through mutagenesis and plasmid display selection, which possess higher affinity and improved recovery of complex N-glycomolecules. In particular, we demonstrate that the Fbs1 GYR variant may be employed for substantially unbiased enrichment of N-linked glycopeptides from human serum. Most importantly, this highly efficient N-glycopeptide enrichment method enables the simultaneous determination of N-glycan composition and N-glycosites with a deeper coverage (compared to lectin enrichment) and improves large-scale N-glycoproteomics studies due to greatly reduced sample complexity.

Protein glycosylation is an essential post-translational modification which analysis is complicated by the diversity of glycan composition and heterogeneity at individual attachment sites. Here the authors describe a method to selectively enrich N-linked glycopeptides to facilitate the detection of micro-heterogeneity in N-glycosylation.