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a) b)
Figure 20. a) Acylphosphatase, 1aps [77]. Example of a plaitfold domain.
CATH
:
3,30,70,100 (alpha beta, 2-layered sandwich, alpha-beta plaits).
SCOP
: a+b,
ferridoxin-like. b) Topology diagram. A βα Greek-Key is outlined in black.
5.4 Predominantly Beta-Domains
Beta-Beta Packing There are two common ways of packing
β
-sheets, aligned and
orthogonal. In aligned packing, two
-segment lie face to face to
form a sandwich with the backbone direction of the upper sheet rotated in the clockwise
direction with respect to the other by an angle that varies from 20
o
to 50
o
depending on the
right-handed twist of the
β
-sheets, but is usually ~ 30
o
. An aligned
β
-sheet is illustrated by
the immunoglobulin fold in figure 24. Orthogonally packed
β
-sheets joined by a non
β
-sheets (figure 21) also lie
face to face but one is at ~90
o
to the other and the strands at one corner or two diagonally
opposite corners have a bend due to a
β
β
-bulge or
β
-coil and pass uninterrupted from one
layer to the next [[9].
Figure 21. α
-Chymotrypsin, 5cha, Cain A,
residues 27-112 [78]. An example of orthogonal
β
-sheet packing, the dark shaded strand has a 90
o
bend as it passes from one layer to the other.
OB (Oligonucleotid/Oligosaccharide Binding) Roll The OB roll consists of a five-
stranded
β
-sheet coiled to form a barrel structure, which may be capped by a
α
-helix.
Examples include heat labile enterotoxin and antifungal protein [79-80].
Jelly Roll.This fold, which forms a 2-layered sandwich, is made up of Greek-key motifs in
which the connection from strand 2 to strand 3 is made between layers and the connection
