Chemistry Reference
In-Depth Information
13
Protein-Carbohydrate Interactions: Basic Concepts and
Methods for Analysis
Dolores Sol í s , Antonio Romero , Margarita Men é ndez , and Jes ú s Jim é nez - Barbero
The structural diversity of carbohydrates underlies the potential of this class of
biomolecules for storing biological information, as explained in Chapter 1 . Turning
this potential into an operative sugar code entails the existence of effi cient decod-
ing devices. As complex carbohydrates decorate the surface of cells, complemen-
tary binding between carbohydrates on neighboring cells is possible, although the
role of direct carbohydrate interactions in biological processes has been reported
in only a few cases (please see Chapter 21). On the contrary, recognition of carbo-
hydrates by proteins has been shown to be central to a myriad of intra- and extra-
cellular physiological and pathological processes (please see Table 19.2 for functions
of animal lectins). Proteins exhibiting carbohydrate-binding ability include sugar-
specifi c antibodies, carbohydrate-active enzymes (which, in addition to the catalytic
module, may also contain non- catalytic carbohydrate - binding modules), transport/
sensor proteins for free sugars and lectins (for defi nition of the term ' lectin ' , please
see Chapter 15). The scope and relevance of these protein- glycan recognition
systems is extensively illustrated throughout this topic. This chapter will focus on
the fundamental structural and thermodynamic features of protein- carbohydrate
interactions revealed by different methodological approaches. A detailed knowl-
edge of the intricacies of carbohydrate recognition by proteins is fundamental to
a rational design of new carbohydrate-based drugs (please see Chapter 28 for
details).
13.1
Atomic Features of Protein- Sugar Interactions
Basic atomic features of protein-sugar interactions stem from the chemical prop-
erties of carbohydrates (Figure 13.1). First, the presence of freely rotatable hydroxyl
groups facilitates the formation of directional hydrogen bonds. The
sp
3
- hybridized
oxygen atom can participate in two hydrogen bonds as acceptor while the proton
can act as donor (Figure 13.1a). Thus, taking into account the abundance of
hydroxyl groups in carbohydrates, a major role of hydrogen bonding is foreseeable.
