Biomedical Engineering Reference
In-Depth Information
Fig. 2.1
Schematic structure
and disulfide bonds of
a / b -gliadins, g -gliadins,
LMW-, and HMW-GS
(Adapted from [
64
] )
The amino acid compositions are characterized by high contents of glutamine, glycine,
and proline. The amino acid sequences [
63
] can be separated into three structural
domains: a nonrepetitive N-terminal domain A of ~100 residues, a repetitive central
domain B of 400-700 residues, and a nonrepetitive C-terminal domain C with ~40
residues (Fig.
2.1
) [
64,
65
]. Domain B is dominated by repetitive sequences such as
QQPGQG (one-letter-code for amino acids) as a backbone with inserted sequences
like YYPTSL, QQG, and QPG with remarkable differences between x- and y-types
(Table
2.5
). Domains A and C have a more balanced amino acid composition and
more amino acid residues with charged side chains. In a native state, the proteins of
the HMW group are aggregated through interchain disulfide bonds (Fig.
2.1
).
The MMW group consists of the homologous w1,2-gliadins of wheat, w -secalins
of rye, and C-hordeins of barley including amino acid residues between 300 and
400 and MW around 40,000 (Table
2.4
). Additionally, wheat contains unique w 5-
gliadins with more than 400 residues and MW around 50,000. This group, likewise,
is not present in oats. The proteins of the MMW group have extremely unbalanced
amino acid compositions characterized by high contents of glutamine, proline, and
phenylalanine, which together account for ~80% of total residues. Most sections of
the amino acid sequences are composed of repetitive units such as QPQQPFP or
QQQFP. This type of protein occurs as monomers and is readily soluble in aqueous
alcohols and, in parts, even in water.
