Chemistry Reference
In-Depth Information
As mentioned in the preceding section, organisms are integrated by a hierarchi-
cal structure in which the basal level is populated by the genome. When it
comes to glycogenes, the following levels are presumed from the basal level: gly-
cogenes, glycan-synthesizing enzymes, glycans (glycoconjugates), supramolecular
assemblies (cell formation), intercellular networks (tissue formation), intertissual
networks (organ formation) and interorganic networks (organism formation)
(Figure 23.1). The relationship between a glycogene and its related glycan-synthe-
sizing enzyme is linear, and has one- to - one correspondence. In contrast, the rela-
tionship between a glycan-synthesizing enzyme and its related glycan is nonlinear,
and has one-to-many correspondence. In other words, glycans are molecules
formed via self-organization. Therefore, inactivation of a glycogene will affect a
number of glycans, which will display complex phenotypes.
Figure 23.1
Hierarchical structure to integrate the organism.
23.2.2
Functional Association of Glycogenes
Although glycans are actual players in the biological events, their remodeling by
means of gene targeting of glycogenes is the best approach to determine their
in
vivo
functions. Several enzymes participate in the biosynthesis of an oligosaccha-
ride, meaning that more than one glycogene is responsible for the formation of
an oligosaccharide. These genes are functionally associated with each other.
This issue is easier to understand if we look at the example of a glycan ligand
involved in lymphocyte homing (please see Chapter 27, especially Figure 27.1, and
also Chapter 29, especially Figure 29.5). Lymphocytes patrol the entire body, pro-
tecting it against infection by circulating between the blood vessels and the lym-
phatic organs. The entry of lymphocytes from the blood vessels to the lymph nodes
is called lymphocyte homing. This homing process is initially mediated by the
interaction between L-selectin on the surface of lymphocytes and its glycan ligand
on the surface of high endothelial venules (HEVs) of lymph nodes. L-Selectin
