# Influence of Structural Features of Peptides on Their Affinity to Cotton Linters Paper

## TL;DR

This study explores how different structural features of peptides affect their binding to cotton linters paper, aiming to improve noncovalent functionalization of cellulose.

## Contribution

The study identifies structural features and modifications that enhance peptide affinity to cellulose, including the role of TAMRA labeling and electrostatic interactions.

## Key findings

- Tyrosine residues are not essential for peptide binding to cotton linters paper, unlike in carbohydrate-binding modules.
- Peptides with TAMRA labeling show increased affinity due to an avidity effect.
- Electrostatic interactions significantly influence peptide affinity, with positively charged groups enhancing binding.

## Abstract

As an alternative to chemical functionalization of cellulose,
fusion
constructs with carbohydrate-binding modules (CBMs) can be used for
the noncovalent immobilization of various compounds and functionalities
on cellulose. Smaller cellulose-binding peptides might be used as
an alternative, as they are easy to modify and can be produced completely
synthetically. To investigate which structural features of peptides
promote binding to cotton linters paper, we have established a label-free
assay to assess paper affinity. Even though tyrosine residues are
essential for the binding of CBMs, we found that the Y/A exchange
in peptides did not lead to a reduction in the affinity. This confirms
previous assumptions that aromatic structures that are needed to orient
CBMs during cellulose binding are less important for smaller, more
flexible peptides. We also show that the aromatic fluorophore 5(6)-carboxytetramethylrhodamine
(TAMRA), which is sometimes used for peptide labeling, leads to an
increase in affinity due to an avidity effect. In addition, we observed
that peptides with a C-terminal carboxylate group
or carboxylate side chains have a lower affinity, and peptides with
positively charged amino groups have a higher affinity than the corresponding
uncharged peptides. We attributed this to electrostatic interactions
with carboxylate groups on the paper. While most peptides tested in
this study bound with K
D values in the
midmicromolar range, the combination of a C-terminal
amide and an N-terminal TAMRA modification yielded
a peptide with affinity to cotton linters paper in the low micromolar
range. The findings presented in this work confirm and expand findings
from previous work and reveal limitations and features that point
the way toward high-affinity peptides for the functionalization of
cellulose.