Chemistry Reference
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(a)
(b)
FIGURE 3.13
-helix, which
form a barrel-like structure. (b) An open twisted
b
-sheet with helices on both sides, such as the coenzyme-binding domain of many dehy-
drogenases. (From
Branden & Tooze, 1991
.
Reproduced with permission from Garland Publishing, Inc.)
(a) Triose phosphate isomerase (TIM) has a
bab
structure made up of 8
ba
motifs terminating in a final
a
FIGURE 3.14
(a) The Cu
e
Zn superoxide dismutase is made up of eight antiparallel
b
-strands; both the constant (b) and variable (c) domains
of immunoglobulins are made up of seven antiparallel
b
-strands with the same topology: the variable domain contains two additional
b
-strands.
(From
Branden & Tooze, 1991
.
Reproduced with permission from Garland Publishing, Inc.)
Triose phosphate isomerase (TIM), a 247-residue enzyme of the glycolytic pathway (Chapter 5), is an example
of the first of the two main classes of
a
/
b
proteins, made up of
beab
motifs. It consists of a core of eight twisted
parallel
b
-strands, arranged close together to form a cylindrical structure, known as a
b
-barrel viewed in
Figure 3.13
a from the top. The
-barrel. This
domain structure is often referred to as the TIM barrel, since it was first found in triose phosphate isomerase. In the
topological represention at the bottom of the figure, the
b
-strands are connected by
a
-helices, located on the outside of the
b
a
-helices are represented by rectangles and the
b
-sheets as
