A BIRD’S-EYE VIEW OF STRUCTURE
AND ASSEMBLY
An idealized picture of a HSPG is shown in
Figure 2. Each proteoglycan consists of a protein
and one or more covalently attached HS chains.
Comprehensive reviews have appeared on the
assembly process and structural characterization
of the chains, and therefore these subjects
will not be discussed further here (Esko and
Selleck 2002; Sugahara and Kitagawa 2002;
Sasisekharan et al. 2006; Ori et al. 2008; Laremore
et al. 2009). However, several features are
important to consider in the context of their
biological activities. (1) HSPGs are polyanionic
and have unusual hydrodynamic volume
because of the presence of long HS chains
(40–300 sugar residues, 20–150 nm), sulfate
groups, and uronic acids. Thus, different
HSPGs often copurify by techniques that rely
simply on the anionic characteristics of the
chains or gel filtration. HS and other sulfated
GAGs are amongst the most highly negatively
charged biopolymers in nature and variation
in the number and length of the chains gives
rise to enormous polydispersity. (2) Some proteoglycans
contain only one GAG chain (e.g.,
CD44v3 and betaglycan), whereas others have