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Holographic particle characterization yields the diameter of individual colloidal spheres with nanometer precision and can resolve probe beads growing as molecules bind to their surfaces. We demonstrate label-free holographic assays for antibodies and for antigenic proteins from pathogenic viruses, including SARS-CoV-2 and H1N1. 

The size of a probe bead reported by holographic particle characterization depends on the proportion of the surface area covered by bound target molecules and so can be used as an assay for molecular binding. We validate this technique by measuring the kinetics of irreversible binding for the antibodies immunoglobulin G (IgG) and immunoglobulin M (IgM) as they attach to micrometer-diameter colloidal beads coated with protein A. These measurements yield the antibodies’ binding rates and can be inverted to obtain the concentration of antibodies in solution. Holographic molecular binding assays therefore can be used to perform fast quantitative immunoassays that are complementary to conventional serological tests. 

Abstract The number of structural studies of peptoids has grown dramatically over the past 20 years. To date, over 100 high‐resolution structures have been reported for peptoids, which are typically defined as N‐substituted glycine oligomers. We have collected these structures and standardized their sequence representations to facilitate structural analysis as the dataset continues to grow. These structures are presented online as The Peptoid Data Bank (databank.peptoids.org), which also provides persistent links to the published structural data. This review analyzes the present collection of structures and finds extensive support for grouping side chains by their chemistry at the position adjacent to the backbone nitrogen. Groups of side chains with similar chemistry at this position show similar influences on the conformational preferences of the backbone. We also observe a relationship between the side chain and backbone conformations for many monomers that has not previously attracted significant discussion: the values of the χ₁and ϕ dihedrals are correlated. We outline a general design strategy for attaining a specific backbone conformation based on the patterns seen in the collected structures. 

Abstract Despite recent progress, it remains challenging to program biomacromolecules to assemble into discrete nanostructures with pre‐determined sizes and topologies. We report here a novel strategy to address this challenge. By using two orthogonal pairs of heterodimeric coiled coils as the building blocks, we constructed six discrete supramolecular assemblies, each composed of a prescribed number of coiled coil components. Within these assemblies, different coiled coils were connected via end‐to‐side covalent linkages strategically pre‐installed between the non‐complementary pairs. The overall topological features of two highly complex assemblies, a “barbell” and a “quadrilateral” form, were characterized experimentally and were in good agreement to the designs. This work expands the design paradigms for peptide‐based discrete supramolecular assemblies and will provide a route for de novo fabrication of functional protein materials.