# Various Ways to Be Negative: Biophysical Characterization of Polyanionic Biomolecules

## TL;DR

This paper explores how different negatively charged biopolymers behave in various environments, revealing how their structure and charge affect their flexibility and function.

## Contribution

The study provides a systematic biophysical comparison of diverse polyanions using molecular dynamics simulations.

## Key findings

- Polyanions show distinct compactness and flexibility depending on their intrinsic features.
- Conformational preferences of polyanions vary with cation type and polymer class.
- Subtle differences in monomer properties lead to unique biophysical behaviors within the same family.

## Abstract

Negatively charged
biopolymers (i.e., polyanions) are ubiquitous
across all domains of life and participate in a vast array of cellular
processes. Their remarkable diversity raises fundamental questions
about how their biophysical properties enable such functional breadth.
To investigate these relationships, we performed all-atom molecular
dynamics simulations of 11 representative polyanions spanning three
major classes of polyanionic biomacromolecules: polynucleotides, polypeptides,
and polysaccharides. Each polymer was modeled at a fixed length of
30 repeat units but differed in monomer size, charge per monomer,
and linear and radial charge density. We systematically examined how
these intrinsic features modulate their biophysical properties and
influence solvent organization and conformational preferences in mono-
and divalent counterion environments. Our analyses reveal that polyanions
differ markedly in compactness and flexibility and that their conformational
preferences respond in a system-specific manner to cation identity.
While some polymers are strongly modulated by sodium or calcium, others
remain comparatively insensitive. Collectively, the polyanions span
a broad landscape of conformational space defined by their intrinsic
features and the resulting biophysical properties, with each macromolecular
family occupying a distinct region of this space. Even within a given
family, subtle differences in intrinsic features lead chemically related
systems to exhibit unique biophysical properties. These findings show
that diverse classes of polyanions possess tunable biophysical properties
that evolution could exploit to support specific biological functions,
and they further highlight the intriguing question of why biological
systems tend to favor polyanions over their positively charged counterparts.