ABSTRACT
Proteins are perhaps one of themost diverse and complex structures
in nature. The functional diversity of proteins is very broad.
Enzymes perform catalytic functions, converting substrates into
products with an incredible speed and specificity compared with
common organic reactions. There are structural proteins in the
cytoskeleton and extracellular matrix that are responsible for
maintaining cell shape, intracellular transport, cell motility, and
cell adhesion. Membrane proteins ormembrane-associated proteins
perform functions such as transport and enzymatic activities. In
addition, there are many examples of proteins that have character-
istic functions and structural roles. Because of such functional and
structural diversity of proteins, it is difficult to capture their im-
portant features within any one classification scheme. Furthermore,
post-translational modifications such as glycosylation, phosphory-
lation, and ubiquitination further complicate the functional and
structural diversity of proteins.
