Biology subjects

Guseman, A.

Publications and source records attributed to Guseman, A..

3 recordsLinked to original sources

bioRxiv2026

Engineered OAA lectins as selective and sensitive high mannose glycan targeting tools

The Oscillatoria agardhii agglutinin (OAA) lectin interacts with N-glycans through a pentamannose core shared among all high mannose N-glycans (HMGs). Because HMGs only differ by number of mannose sugars, there is a scarcity of tools sensitive enough to resolve each specific HMG structure in their biological context. Here, we investigate the sequence space of OAA to tune the binding properties towards selectivity of Man5GlcNAc2, thus generating a structure-specific detection tool. Using phage display to screen a diverse library of OAA variants, we identify a variant with high selectivity for Man5GlcNAc2 that we further dissect to reveal four mutations necessary for selectivity and two mutations responsible for enhanced affinity for all HMGs. Coupling a crystal structure of the selective variant with binding analysis of specific point mutations, we reveal how co-dependent mutations achieve selectivity. We then demonstrate how variants can be valency-modulated on a single beta-barrel scaffold to improve their binding properties by orders of magnitude. Finally, we showcase the applicability of engineered OAA variants as improved HMG profiling tools and tunable antiviral agents.

biophysics↗

bioRxiv2025

Glycopolymers stabilize protein folding and protein-protein interactions via enthalpic interactions

Macromolecular crowding is ubiquitous to physiological environments, perturbing the thermodynamics and kinetics of proteins via excluded volume and nonspecific chemical interactions. While crowding has been well-studied in vitro and in cells, the inert sugar polymers used to simulate crowding lack the chemical characteristics of biomolecules. Emerging studies guide the development of more relevant models of crowding in the cell, but little work has been done to discern crowding effects on proteins at the cell surface. Using 19F NMR, we measure how protein stability, folding, and intermolecular interactions are modulated by three glycopolymers abundant at the cellular exterior. Biologically relevant glycopolymers including heparin, hyaluronic acid, and mucin significantly stabilize folding of the N-terminal domain of the Drk-SH3 protein. These interactions are enthalpically stabilizing, emphasizing the importance of chemical interactions for biologically relevant crowders. We further show that these glycopolymers stabilize a homodimer formed by the A34F variant of GB1, demonstrating that biological crowders not only affect isolated proteins, but also influence how proteins interact with one another. Crowding is more complex than simple ideas of volume exclusion suggest, and our work guides a more comprehensive understanding of protein crowding in the context of the glycocalyx, the last frontier of the cell.

biophysics↗

bioRxiv2022

The Molecular and Evolutionary Principles of Histone Folding in Eukarya and Archaea

Histones are the dominant proteins to compact and store DNA in both Eukarya and Archaea. For a long time, histones are observed to exist in the unit of dimers but diverge into different formats such as heterodimers in Eukarya or homodimers in Archaea. Here, by studying 11 types of histone proteins, both monomers and their dimeric complexes, using multiscale molecular dynamics (MD) simulations combined with NMR and circular dichroism experiments, we confirm the widely applied "folding upon binding" mechanism of histone structures. A histone dimer appears to form the longest 2 helices followed by other shorter helices and inter-molecular tertiary structures. We report an alternative conformation, namely, the inverted non-native dimer, which has a minimum free energy state. Protein sequence analysis indicates that the inverted conformation can be attributed to a hidden head-tail sequence symmetry underlying all histone proteins. This finding strongly support previously proposed histone evolution hypotheses. Finally, we separately used the MD-based AWSEM and AI-based AlphaFold-Multimer model to predict eukaryotic histone homodimer structures and performed extensive allatom MD simulations to examine their structural stabilities. Our results suggest that eukaryotic histones can also form stable homodimers, whereas their disordered tails-- the structurally asymmetrical region--may tip the balance towards the formation of heterotypic dimers.

biophysics↗