Chemistry Reference
In-Depth Information
Figure 16.1
Continued
16.1 d), only one Ca
2+
is present in this module, and this one at the edge of the
β
-sandwich (Figure 16.1e). Akin to the situation in leguminous lectins, the Ca
2+
-
binding site appears preformed by four amino acid side-chains, one water mole-
cule and, notably, an inorganic sulfate ion to complete an octahedral coordination
[11]. The rather small distance of 2.5 Å between Ca
2+
and SO
2−
prompts to suspect
an association with anionic carbohydrates or
- dystroglycan
in vivo
at this site [11,
12]. The latter interaction is pivotal for the integrity of the dystrophin-glycoprotein
complex, because aberrations lead to muscular dystrophy [13] (Figure 22.4 ; for
summary table on plant/animal lectins with
α
-sandwich fold, please see Table 18.2
and Table 19.1). Heparin is a known ligand for this module (for structure of the
anticoagulant pentasaccharide, please see Figure 1.7 (bottom panel); for an over-
view on proteoglycans, please see Chapter 11 and for therapeutic application, see
Chapter 28.5). How this type of glycosaminoglycan and Ca
2+
act in concert to
facilitate tight binding to a protein is illustrated by the case of annexin A2.
β
