glands of all lactating mammals which produce
lactose or lactose-derived oligosaccharides (Marsupialia), and is also released into the blood. It is
not found in the milk glands and milk of aquatic
mammals which do not produce lactose. The distribution and function of the ~-Iactoglobulins
remains a mystery. They are found only in the milk
of ruminants, the horse, ass, pig, dog, dolphin
(Tursiops truncatus) , manatee (Trichechus manatus) and kangaroo, and their occurrence in human
milk is controversial [97]. In the horse, ass, pig,
dog, dolphin and manatee they are monomeric
proteins, but they are dimeric in the ruminants and
the kangaroo. The horse and the dolphin have two
~-lactoglobulins with very different sequences,
and the cat actually has three lactoglobulin loci
(I-III) [49, 97]. The ~-lactoglobulins of the ruminants agree with each other by more than 90 % but
with those of other mammals by only 30-55 %
[49]. The polypeptide chains of 155-166 amino
acids have a spatial structure of two layers of antiparallel folded sheets, similar to that of the retinolbinding proteins of vertebrate blood, the bilinbinding protein of insect haemolymph, and other
transport proteins for hydrophobic molecules in
the protein super-family of the lipocalins. Pairwise
sequence comparisons within the family show
agreements of 25-30 % [41].
The acidic whey proteins (WAP) are unusual
milk proteins in that they are found only in the
milk of the rat, mouse and rabbit, and occur at
concentrations many times higher than that of the
a-Iactalbumins. In the milk glands ofthe lactating
rat, WAP mRNA makes up no less than 15 % of
the total poly(A)-RNA; this protein is not found
at all in the ruminants. The WAP genes of the
mouse and rat are highly homologous; they coincide over a sequence which begins 325 bp
upstream of the cap-binding site and extends
20 bp into the 3'-flanking region. The conservative evolution of this 5' region probably involves
selection for a similar hormone-regulating
mechanism. However, the rat, mouse and rabbit
amino acid sequences (127-137 amino acids)
show at most 64 % agreement [26].
11.7 Proteins of the Arthropod Cuticula
The arthropod cuticula is an extracellular structure secreted by the underlying epidermis. It is
made up in a complex manner from several layers
that differ in both fine structure and composition.
11. 7 Proteins of the Arthropod Cuticula
391
Exterior to the procuticula (endo- and exocuticula) of at least 100 !lm lies the multilayered epicuticula of only 1-2 !lm. The epicuticula is chitinfree but its molecular structure is otherwise
largely unknown. The procuticula consists of achitin fibres in a protein matrix. Depending on its
exact function, the pro cuticula may be hard, flexible or elastic. As will be described in more detail
in Chapter 12, the hardening (sclerotization) of
the cuticula, which is usually accompanied by a
brown coloration, involves the cross-linking of
protein molecules by phenolic substances. As the
proteins are then no longer extractable, examination of the cuticula proteins of the insects has
been restricted almost entirely to the nonsclerotized cuticula, i.e. that of larvae, pupae,
and hatching or freshly hatched adults.
The insect cuticula typically consists of many
different proteins, the number of which varies
greatly according to the separation and detection
methods used. The differences in complexity of
the cuticula protein spectrum between the various insect orders will only be appreciated fully
after a large number of insect species have been
compared using the same method. Twodimensional electrophoresis of extractable cuticula proteins from the locusts Locusta migratoria
and Schistocerca gregaria gives more than
100 spots, most of which occupy the same position in both species [3]. Translation of the
mRNAs from wing epithelium of the moth Manduca sexta gave 160 different polypeptides in the
pupa and 120 in the adult; only some of these had
similar values for molecular size and pI in both
developmental stages [120]. Simpler electrophoretic or chromatographic methods reveal only
about 10-20 different extractable cuticula proteins [3, 118, 121, 135]. The protein spectrum is
unusually simple in the fly Ceratitis capitata,
where more than 80 % of the total protein from
pupal cuticula consists of one glycoprotein of
about 100 kDa [10]. The variety of cuticula proteins varies not only with the species but also with
the developmental stage within a species [65, 88,
118, 121, 135]. In many species, even different
regions of the cuticula of one individual show differences in the protein spectrum.
Despite all these differences, cuticula proteins
have quite a few common features. They are usually very small, with masses of 8-37 kDa. About
40 % of the total cuticula protein of Drosophila
consists of one component of 90 kDa, which is
covalently bound to chitin and has prophenoloxidase and peroxidase activity [53]. The predominant proteins of many species are acidic with pI
lactose or lactose-derived oligosaccharides (Marsupialia), and is also released into the blood. It is
not found in the milk glands and milk of aquatic
mammals which do not produce lactose. The distribution and function of the ~-Iactoglobulins
remains a mystery. They are found only in the milk
of ruminants, the horse, ass, pig, dog, dolphin
(Tursiops truncatus) , manatee (Trichechus manatus) and kangaroo, and their occurrence in human
milk is controversial [97]. In the horse, ass, pig,
dog, dolphin and manatee they are monomeric
proteins, but they are dimeric in the ruminants and
the kangaroo. The horse and the dolphin have two
~-lactoglobulins with very different sequences,
and the cat actually has three lactoglobulin loci
(I-III) [49, 97]. The ~-lactoglobulins of the ruminants agree with each other by more than 90 % but
with those of other mammals by only 30-55 %
[49]. The polypeptide chains of 155-166 amino
acids have a spatial structure of two layers of antiparallel folded sheets, similar to that of the retinolbinding proteins of vertebrate blood, the bilinbinding protein of insect haemolymph, and other
transport proteins for hydrophobic molecules in
the protein super-family of the lipocalins. Pairwise
sequence comparisons within the family show
agreements of 25-30 % [41].
The acidic whey proteins (WAP) are unusual
milk proteins in that they are found only in the
milk of the rat, mouse and rabbit, and occur at
concentrations many times higher than that of the
a-Iactalbumins. In the milk glands ofthe lactating
rat, WAP mRNA makes up no less than 15 % of
the total poly(A)-RNA; this protein is not found
at all in the ruminants. The WAP genes of the
mouse and rat are highly homologous; they coincide over a sequence which begins 325 bp
upstream of the cap-binding site and extends
20 bp into the 3'-flanking region. The conservative evolution of this 5' region probably involves
selection for a similar hormone-regulating
mechanism. However, the rat, mouse and rabbit
amino acid sequences (127-137 amino acids)
show at most 64 % agreement [26].
11.7 Proteins of the Arthropod Cuticula
The arthropod cuticula is an extracellular structure secreted by the underlying epidermis. It is
made up in a complex manner from several layers
that differ in both fine structure and composition.
11. 7 Proteins of the Arthropod Cuticula
391
Exterior to the procuticula (endo- and exocuticula) of at least 100 !lm lies the multilayered epicuticula of only 1-2 !lm. The epicuticula is chitinfree but its molecular structure is otherwise
largely unknown. The procuticula consists of achitin fibres in a protein matrix. Depending on its
exact function, the pro cuticula may be hard, flexible or elastic. As will be described in more detail
in Chapter 12, the hardening (sclerotization) of
the cuticula, which is usually accompanied by a
brown coloration, involves the cross-linking of
protein molecules by phenolic substances. As the
proteins are then no longer extractable, examination of the cuticula proteins of the insects has
been restricted almost entirely to the nonsclerotized cuticula, i.e. that of larvae, pupae,
and hatching or freshly hatched adults.
The insect cuticula typically consists of many
different proteins, the number of which varies
greatly according to the separation and detection
methods used. The differences in complexity of
the cuticula protein spectrum between the various insect orders will only be appreciated fully
after a large number of insect species have been
compared using the same method. Twodimensional electrophoresis of extractable cuticula proteins from the locusts Locusta migratoria
and Schistocerca gregaria gives more than
100 spots, most of which occupy the same position in both species [3]. Translation of the
mRNAs from wing epithelium of the moth Manduca sexta gave 160 different polypeptides in the
pupa and 120 in the adult; only some of these had
similar values for molecular size and pI in both
developmental stages [120]. Simpler electrophoretic or chromatographic methods reveal only
about 10-20 different extractable cuticula proteins [3, 118, 121, 135]. The protein spectrum is
unusually simple in the fly Ceratitis capitata,
where more than 80 % of the total protein from
pupal cuticula consists of one glycoprotein of
about 100 kDa [10]. The variety of cuticula proteins varies not only with the species but also with
the developmental stage within a species [65, 88,
118, 121, 135]. In many species, even different
regions of the cuticula of one individual show differences in the protein spectrum.
Despite all these differences, cuticula proteins
have quite a few common features. They are usually very small, with masses of 8-37 kDa. About
40 % of the total cuticula protein of Drosophila
consists of one component of 90 kDa, which is
covalently bound to chitin and has prophenoloxidase and peroxidase activity [53]. The predominant proteins of many species are acidic with pI