Mapping complex biopolymer structures by AFM

A.N. Round*, M. Berry#, T.J. McMaster*, A.P. Corfield⁺ and M.J. Miles*

* H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL,
# Mucin Research Group, University of Bristol, Bristol Eye Hospital, Bristol BS1 2LX
+ Division of Medicine, Mucin Research Group, Bristol Royal Infirmary, Bristol BS2 8HW

Atomic Force Microscopy (AFM) is a powerful tool with which to map the structure and function of complex, irregular biopolymers such as mucin. High-resolution AFM has been used to image intact human ocular mucins in both air and a near-physiological buffer, with the aim of investigating the size distribution and conformation of the mucin population. We demonstrate that AFM can be used to determine the length distributions of both the native biopolymer sample and the products of its controlled disassembly, and that valid estimates of the persistence length can be obtained from simple treatments of AFM image data.
We also consider the potential of resonance-controlled Tapping Mode AFM imaging to investigate changes in molecular thickness (indicating oligosaccharide branches) and the use of phase imaging to detect differences in charge distribution along individual polymers.