Chemistry Reference
In-Depth Information
Systematic audits of CTLDcps are reported for model organisms representing
invertebrates (worm:
Caenorhabditis elegans
[5, 11] ; fl y/insect:
Drosophila melano-
gaster
[6]) and vertebrates (human [7]; fi sh:
Fugu rubripes
[8] ). More restricted
analyses focused on immune system CTLDcps have been reported for a urochor-
date (sea squirt:
Ciona intestinalis
[12]) and a protochordate (echinoderm/purple
sea urchin:
Strongylocentrotus purpuratus
[13]). Also for sea urchin, a distinctive
suite of genes having in common a CTLD evolved to construct the unique biomin-
eral structure of the endoskeletal tissue called the stereom has been analyzed [14].
Description of glycosylation in these model organisms which complements the
lectin analysis is given in Chapter 7. Vertebrate genome sequences are also avail-
able for a representative bird, amphibian, monotreme and marsupial, and increas-
ingly multiple genome sequences for some branches, especially mammals (mouse,
rat, dog, cow) and other animals of commercial importance (for example honey
bee).
These studies have confi rmed that only the 'tip of the iceberg' of the variety of
CTLDcps had been gleaned by the traditional experimental approach. The main
conclusions are:
•
The CTLD is indeed very common but its relative and absolute abundance
varies. For example, it is particularly abundant in
C. elegans
with 125 CTLDcps
([5] and more recently 278 CTLDcps [11]), 52 of them with more than one CTLD,
whereas in
Drosophila
only 32 CTLDcps were found, all but one containing only
one CTLD [6]. In a typical vertebrate (human), 66 CTLDcps with 96 CTLDs were
found [7] .
•
A high proportion of the CTLDs in the invertebrate CTLDcps lack the sequence
signature correlated with carbohydrate-binding capacity discussed above (85%
in
C. elegans
and 81% in
Drosophila
[2], whereas about half of the vertebrate
CTLDs are classed as CRDs (that is predicted to bind carbohydrate [7] ).
•
Whereas there is strong conservation of the groups within the vertebrate lineage,
there is little or no similarity between vertebrate and invertebrate CTLDcps in
their domain organization. This is illustrated in Figure 20.2, where it may also
be seen that vertebrate CTLDcps contain a greater variety of other domains than
do invertebrate CTLDcps.
•
Furthermore, attempts to construct phylogenetic trees from sequence analysis
of CTLDs of CTLDcps from evolutionarily distant Metazoan branches (for
example human, worm and fl y CTLDcps) has been unsuccessful. This has led to
the conclusion that the repertoire of CTLDcps has evolved independently in the
main Metazoan lineages starting from one or a small number of primordial
CTLDs. These have been 'crafted' to create the repertoire of CTLDcps with
CTLD specifi cities for lineage-adapted functions, as observed from whole-
genome analysis [2, 3] .
•
A consequence of this evolutionary complexity is that in cases where a similar
carbohydrate-binding function can be attributed to CTLDcps from widely distant
Metazoan branches it is diffi cult to discriminate divergent from convergent
