Burton, A. J. | bioRxiv Science

bioRxiv2019

Differential and Age Dependent Expression of Specific Sialoglycans on HeLa Cells -Revealed by Direct Fluorescent Glycan Labeling

Cells are covered with glycans. The expression and distribution of specific glycans on cell surface are important for various cellular functions. Imaging these glycans is essential to elucidate their biological roles. Here, utilizing enzymatic incorporation of fluorophore-conjugated sialic acids, dubbed as direct fluorescent glycan labeling (DFGL), we report the imaging of N- and O-glycans and particularly tumor specific sialyl T antigen on HeLa cells. It is found that while Core-1 O-glycans are relatively evenly distributed on cells, the expression of N-glycans tend to be more peripheral. More interestingly, the expression of sialyl T antigen displays random and sporadic patterns. In technique side, DFGL allows convenient labeling or imaging of various glycans on intact glycoproteins or cell surfaces with variety of fluorescent dyes.

cancer biology↗

bioRxiv2018

Navigating the structural landscape of de novo α-helical bundles

The association of amphipathic helices in water leads to -helical-bundle protein structures. However, the driving force for this--the hydrophobic effect--is not specific and does not define the number or the orientation of helices in the associated state. Rather, this is achieved through deeper sequence-to-structure relationships, which are increasingly being discerned. For example, for one structurally extreme but nevertheless ubiquitous class of bundle--the -helical coiled coils--relationships have been established that discriminate between all-parallel dimers, trimers and tetramers. Association states above this are known, as are antiparallel and mixed arrangements of the helices. However, these alternative states are less-well understood. Here, we describe a synthetic-peptide system that switches between parallel hexamers and various up-down-up-down tetramers in response to single-amino-acid changes and solution conditions. The main accessible states of each peptide variant are characterized fully in solution and, in most cases, to high-resolution X-ray crystal structures. Analysis and inspection of these structures helps rationalize the different states formed. This navigation of the structural landscape of -helical coiled coils above the dimers and trimers that dominate in nature has allowed us to design rationally a well-defined and hyperstable antiparallel coiled-coil tetramer (apCC-Tet). This robust de novo protein provides another scaffold for further structural and functional designs in protein engineering and synthetic biology.

biochemistry↗