Chemistry Reference
In-Depth Information
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In 1907, H.V. Wilson observed a remarkable phenomenon in which dissociated
marine sponge cells from two different species reaggregated according to their
species of origin to form clones of the parent sponge. This pioneering assay
was the fi rst experimental demonstration of cell recognition in the animal
kingdom. It is only fi tting that the fi eld that focuses on the organization of
multicellular organisms was born by studying the oldest multicellular animal
on Earth. Aristotle, who fi rst noted that sponges are animals, writes in his
History of Animals
(350 BC): 'Sponges … get their nutriment in slime: a proof
of this statement is the fact that when they are fi rst secured they are found to
be full of slime. … It is said that the sponge is sensitive; and as a proof of this
statement they say that if the sponge is made aware of an attempt being made
to pluck it from its place of attachment it draws itself together, and it becomes
a diffi cult task to detach it'. More than two millennia later, such strong adhesion
was found to be mediated by the carbohydrate structures in sponge AFs.
And almost a century after Wilson's experiment, the aggregation specifi city
of sponge cells was found to reside in the carbohydrate portion of the
sponge cell-surface proteoglycans (the
slime
described by Aristotle) - the fi rst
experimental demonstration of species- specifi c carbohydrate - carbohydrate cell
recognition.
The fi rst report addressing the species specifi city of a carbohydrate- carbohydrate
interaction has shown that recognition between g200 glycans on opposite cells
mediates species - specifi c recognition between live sponge cells (reviewed in [1] ).
According to the current model of carbohydrate- dependent cell - cell recognition,
the AF is bound via its arms onto the cell surface through a Ca
2+
- independent
protein-carbohydrate interaction between a cell-surface receptor and the g6 glycan
(Figure 21.2c). This structure interacts with an identical counterpart on a different
cell through a Ca
2+
- dependent species - specifi c carbohydrate - carbohydrate interac-
tion between g200 glycans.
Compositional and possibly architectural differences between carbohydrate
chains of sponge proteoglycans contribute to the specifi city of the self-interaction
(discussed in [1]). Sponge glycans contain Gal, Fuc, Man, GlcNAc, GalNAc and
GlcA (see Chapter 1 for abbreviations). The composition of glycans from different
individuals of the same species is similar, whereas sponge proteoglycans from
different species display major differences in their carbohydrate display. These
molecules present novel and species-specifi c sequences, particularly sulfated and
branched pyruvylated structures.
Adhesive forces between individual g200 molecules, as measured by AFM, are
in the range of 200-300 pN [1]. These are the strongest forces reported to date for
direct carbohydrate-carbohydrate interactions. This study provided the fi rst indica-
tion that the strength of specifi c glycan self-interactions is comparable to protein-
protein interactions, e.g. in antibody-antigen recognition. Furthermore, surface
