Oligosaccharides as Informational Molecules?

Michael Dorsett Onken mdonken at artsci.wustl.edu
Fri Sep 4 15:13:38 EST 1998


Matt Sandel (mjs419 at psu.edu) wrote:
:     Today in Biology class my professor said that polysaccharides are
: not ever informational molecules.  However, last year, my high school
: biology teacher had mentioned in class that they had discovered that
: some cells have Oligosaccharide chains attached to the outside of their
: cell membranes and that these have cell identification functions.  My
: questions are thus 1) Is this statement regarding Oligosaccharides true?
: And 2) If so, does that make these Oligosaccharides informational
: molecules?  Thanks.
: Matt Sandel

Your professor may have been referring to FREE oligosaccharides being used
for signalling... I hope.  Otherwise, you are correct that the sugar
moieties decorating proteins are absolutely informational.  The immune
system depends on glycosylation for much of its recognition machinery (the
ABO and Rh blood groups are oligosaccharides), and recent work has even
suggested that changes in the oligosaccharides on certain membrane
proteins are responsible for memory (see below)

        Authors
          Fox GB.  O'Connell AW.  Murphy KJ.  Regan CM.
         Institution
          Department of Pharmacology, University College, Belfield,
          Dublin, Ireland.
         Title
          Memory consolidation induces a transient and time-dependent
          increase in the frequency of neural cell adhesion molecule
          polysialylated cells in the adult rat hippocampus.
         Source
          Journal of Neurochemistry.  65(6):2796-9, 1995 Dec.
         Abstract
          Animals trained in a passive avoidance task exhibit a
          transient time-dependent increase in hippocampal neural
          cell adhesion molecule (NCAM) polysialylation at 12-24 h
          following the initial learning trial. Using
          immunocytochemical techniques with a monoclonal antibody
          that specifically recognises NCAM-polysialic acid
          homopolymers, a distinct population of granule-like cells,
          at the border of the granule cell layer and the hilus in
          the dentate gyrus of the adult rat hippocampus, has been
          demonstrated to exhibit time-dependent change in frequency
          at 10-12 h following the initial learning of a one-trial,
          step-through, passive avoidance response. These changes
          were paradigm specific as they failed to occur in those
          animals rendered amnesic with scopolamine. These
          polysialylated dentate neurons are not de novo granule cell
          precursors as administration of 5-bromo-2'-deoxyuridine
          every 2 h from the point of learning to the 12-h
          posttraining time showed no significant difference between
          trained and passive animals in the small number of
          heterogeneously distributed, labelled cells. These findings
          directly identify a morphological substrate of memory,
          implied by previous correlative and interventive studies on
          NCAM function.

In a nutshell, learning can be correlated to the appearance of polysialic
acid (oligosaccharides) moieties decorating the NCAM (a membrane protein)
expressed by cells in the hippocampus (part of the limbic system of the
brain, involved in memory and learning).  [Another paper from several
years back demonstrated that removal of NCAM from these cells produced
mice that couldn't learn to swim a water maze as compared to wild type
mice.]

There are volumes of research on saccharides and their importance to
signalling and targetting - heck, from a purely chemical perspective, DNA
and RNA are just polysaccharides decorated with purines and pyrimidines.

--
Mike Onken        -. .-.   .-. .-.   .  E-mail:
Molecular Cell    ||X|||\ /|||X|||\ /|   mdonken at artsci.wustl.edu
Biology Program   |/ \|||X|||/ \|||X||  URL:
Washington Univ.  '   `-' `-'   `-' `-   http://madsci.wustl.edu/




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