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Glycobiology Advance Access published online on September 21, 2006
Glycobiology, doi:10.1093/glycob/cwl056
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© The Author 2006. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org
Received June 23, 2006
Revised August 30, 2006
Accepted September 19, 2006

Article

Structure-Function Relationships with a T cell Activating Polysaccharide Antigen using Circular Dichroism

Lori S.C. Kreisman 1, Julia H. Friedman 1, Andreea Neaga 1, and Brian A. Cobb 2 *

1 Department of Pathology, Case Medical School, Cleveland, OH
2 Department of Pathology, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106-7288

* To whom correspondence should be addressed.
Brian A. Cobb, E-mail: brian.cobb{at}case.edu


  Abstract

Studies centered on understanding how molecular structure effects biological function have historically focused on proteins. Circular dichroism (CD) is commonly used to analyze protein secondary structure, yet its application to other molecules is far less explored. In fact, little is known about how glycan conformation might effect function, likely due to a lack of tools for measuring dynamic structural changes of carbohydrates. In the present study, we developed a method based on CD to monitor conformational changes in the zwitterionic T cell-activating glycoantigen PSA. We found that PSA helical structure produces a CD spectrum that is strikingly similar to proteins rich in {alpha}-helical content and is equally sensitive to non-polar solvents. Like conventional T cell-dependent proteins, PSA requires processing before class II major histocompatibility complex (MHCII) binding. CD spectra of PSA fragments of varying sizes indicated that fragments smaller than three repeating units lack helical content and is incapable of MHCII binding. Likewise, neutralization of charged groups in the repeating unit resulted in major conformational changes as measured by CD, which correlated to a lack of MHCII presentation. These data represent two significant findings: CD can be used to measure conformational changes in carbohydrates, and the functional epitope from PSA is dependent upon a specific conformation that is stabilized by adjacent repeating units and a zwitterionic charge motif. As a result, this work demonstrates that CD is a valuable tool for use in functional glycomics efforts that seek to align chemical and conformational structure with biological activity.

Keywords: circular dichroism; conformation; glycoantigen; MHC class II; polysaccharide.
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