242
6 Immunoproteins
complete copies and two with slight changes; it is
noteworthy that the surface protein of another
cell parasite, the circumsporozoite protein (CSP)
of the malarial agent, also has a repetitive structure [137]. The forms of the genus Leishmania
that live in insects (promastigotes) all possess the
surface protein P63, which is anchored in the
membrane via the same phosphoglycolipid as
occurs in the VSGs from Trypanosoma. The proteins from five different species of Leishmania
have the same peptide pattern, i.e. P63 is
extremely conserved in evolution. There is immunological evidence for P63 in the vertebrate forms
of Leishmania (amastigotes), but it is not located
on the cell surface, probably due to the absence
of the anchoring lipid [82].
In the malarial agents of the genus Plasmodium, it is the proteins on the surface of the infectious sporozoites, the CSPs, which are probably
important for the interaction with erythrocyte
membranes. There is only one CSP gene, but the
evolutionary alterations of the CSPs are so rapid
as to radically hinder serum therapy for malaria;
each inoculation results in the selection of insensitive variants. The CSP genes from various Plasmodium species have been sequenced. The primary translation product is a polypeptide of
350-370 amino acids and carrys a signal sequence
at the N-terminus and a sequence for membrane
anchorage at the C-terminus. The central region
is made up of repeats of 9-11 amino acids, of
which both the number and sequence vary
between different lines in a species [37]. This
variable region is flanked by two regions which
are similar in all species. Region II apparently
includes the erythrocyte attachment site with the
critical sequence - VTCG - [145]. Whilst the surface of the sporozoites has only CSPs, the
merozoite surface bears many immunodominant
proteins of which only one species has been
sequenced [40]. Immunogenic surface proteins
with repetitive sequences are characteristic of
parasitic protozoans; apart from Trypanosoma
cruzi, Leishmania major and various Plasmodium
species, such proteins have been found on the
merozoites of Eimeria acervulina, a gut parasite
of the chicken [83].
The surface of various Paramecium species is
covered by a layer of large glycoprotein molecules
which together make up about 3 % of the total cell
protein. Because Paramecium can be immobilized
and killed by antisera raised against their surface
glycoproteins, the proteins have, rather unfortunately, been named immobilization-antigens
(i-ags). They consist of a family of related proteins
of about 300 kDa which are anchored in the membrane via glycosylinositol phospholipid [26]. The
i-ags are specific to each Paramecium strain, after
which they are named; for example, the 11 i-ags
from strain 51 of P. tetraurelia are designated 51A
to 51K. Each i-ag is encoded by a single gene but
only one such gene is expressed in a strain at any
one time. Environmental conditions, e.g. temperature or pH, have a strong influence on gene
expression. Several i-ag genes have been
sequenced and found to contain no introns. So,
for example, the 156G gene of P. primaurelia consists of an uninterrupted coding sequence of
8145 bp; the polypeptide of 2715 amino acids has
a marked periodic structure. As in almost all ciliate genes, TAA and TAG code for glutamine, and
only TGA codes for "stop" [57, 140].
References
1. Akerst6m B.: Immunological analysis of almicro globulin in different mammalian and chicken
serum. al-Microglobulin is 5-8 kilodaltons larger in
primates. J. bioI. Chern. 260: 4839-44 (1985)
2. Alexandre S. et a1.: Putative genes of a variantspecific antigen gene transcription unit in Trypanosoma brucei. Mol. cell. BioI. 8: 2367-78 (1988)
3. Amemiya C. T., Haire R. N. and Litman G. w.: Nucleotide sequence of a cDNA encoding a third distinct
Xenopus immunoglobulin heavy chain. Nucleic Acids
Res. 17: 5389 (1989)
4. Amemiya C. T. and Litman G. W.: Complete nucleotide sequence of an immunoglobulin heavy-chain
gene and analysis of immunoglobulin gene organization in a primitive teleost species. Proc. Nat. Acad.
Sci. USA 87: 811-815 (1990)
5. Anderson H.: Adhesion molecules and and animal
development (Review). Experientia 46: 2-13 (1990)
6. Arai K. I. et a1.: Cytokines: Coordinators of immune
and inflammatory responses. Annual Rev. Biochem.
59: 783-836 (1990)
7. Bazan J. R: Structural design and molecular evolution of a cytokine receptor superfamily. Proc. Nat.
Acad. Sci. USA 87: 6934-38 (1990)
8. Beale D.: A comparison of the amino acid sequences
of the extracellular domains of the immunoglobulin
superfamily. Possible correlations between conservancy and conformation (Review). Compo Biochem.
Physio1. Pt. B 80: 181-194 (1985)
9. Beck G. et a1.: Characterization of interleukin-l
activity in tunicates. Compo Biochem. Physio1. Pt. B
92: 93-98 (1989)
10. Becker R. S. and Knight K. L.: Somatic diversification of immunoglobulin heavy chain VDJ genes.
Evidence for somatic conversion in rabbits. Cell 63:
987-997 (1990)
11. Bentley D. R.: Primary structure of human complement component C2. Homology to two unrelated
protein families. Biochem. J. 239: 339-345 (1986)
6 Immunoproteins
complete copies and two with slight changes; it is
noteworthy that the surface protein of another
cell parasite, the circumsporozoite protein (CSP)
of the malarial agent, also has a repetitive structure [137]. The forms of the genus Leishmania
that live in insects (promastigotes) all possess the
surface protein P63, which is anchored in the
membrane via the same phosphoglycolipid as
occurs in the VSGs from Trypanosoma. The proteins from five different species of Leishmania
have the same peptide pattern, i.e. P63 is
extremely conserved in evolution. There is immunological evidence for P63 in the vertebrate forms
of Leishmania (amastigotes), but it is not located
on the cell surface, probably due to the absence
of the anchoring lipid [82].
In the malarial agents of the genus Plasmodium, it is the proteins on the surface of the infectious sporozoites, the CSPs, which are probably
important for the interaction with erythrocyte
membranes. There is only one CSP gene, but the
evolutionary alterations of the CSPs are so rapid
as to radically hinder serum therapy for malaria;
each inoculation results in the selection of insensitive variants. The CSP genes from various Plasmodium species have been sequenced. The primary translation product is a polypeptide of
350-370 amino acids and carrys a signal sequence
at the N-terminus and a sequence for membrane
anchorage at the C-terminus. The central region
is made up of repeats of 9-11 amino acids, of
which both the number and sequence vary
between different lines in a species [37]. This
variable region is flanked by two regions which
are similar in all species. Region II apparently
includes the erythrocyte attachment site with the
critical sequence - VTCG - [145]. Whilst the surface of the sporozoites has only CSPs, the
merozoite surface bears many immunodominant
proteins of which only one species has been
sequenced [40]. Immunogenic surface proteins
with repetitive sequences are characteristic of
parasitic protozoans; apart from Trypanosoma
cruzi, Leishmania major and various Plasmodium
species, such proteins have been found on the
merozoites of Eimeria acervulina, a gut parasite
of the chicken [83].
The surface of various Paramecium species is
covered by a layer of large glycoprotein molecules
which together make up about 3 % of the total cell
protein. Because Paramecium can be immobilized
and killed by antisera raised against their surface
glycoproteins, the proteins have, rather unfortunately, been named immobilization-antigens
(i-ags). They consist of a family of related proteins
of about 300 kDa which are anchored in the membrane via glycosylinositol phospholipid [26]. The
i-ags are specific to each Paramecium strain, after
which they are named; for example, the 11 i-ags
from strain 51 of P. tetraurelia are designated 51A
to 51K. Each i-ag is encoded by a single gene but
only one such gene is expressed in a strain at any
one time. Environmental conditions, e.g. temperature or pH, have a strong influence on gene
expression. Several i-ag genes have been
sequenced and found to contain no introns. So,
for example, the 156G gene of P. primaurelia consists of an uninterrupted coding sequence of
8145 bp; the polypeptide of 2715 amino acids has
a marked periodic structure. As in almost all ciliate genes, TAA and TAG code for glutamine, and
only TGA codes for "stop" [57, 140].
References
1. Akerst6m B.: Immunological analysis of almicro globulin in different mammalian and chicken
serum. al-Microglobulin is 5-8 kilodaltons larger in
primates. J. bioI. Chern. 260: 4839-44 (1985)
2. Alexandre S. et a1.: Putative genes of a variantspecific antigen gene transcription unit in Trypanosoma brucei. Mol. cell. BioI. 8: 2367-78 (1988)
3. Amemiya C. T., Haire R. N. and Litman G. w.: Nucleotide sequence of a cDNA encoding a third distinct
Xenopus immunoglobulin heavy chain. Nucleic Acids
Res. 17: 5389 (1989)
4. Amemiya C. T. and Litman G. W.: Complete nucleotide sequence of an immunoglobulin heavy-chain
gene and analysis of immunoglobulin gene organization in a primitive teleost species. Proc. Nat. Acad.
Sci. USA 87: 811-815 (1990)
5. Anderson H.: Adhesion molecules and and animal
development (Review). Experientia 46: 2-13 (1990)
6. Arai K. I. et a1.: Cytokines: Coordinators of immune
and inflammatory responses. Annual Rev. Biochem.
59: 783-836 (1990)
7. Bazan J. R: Structural design and molecular evolution of a cytokine receptor superfamily. Proc. Nat.
Acad. Sci. USA 87: 6934-38 (1990)
8. Beale D.: A comparison of the amino acid sequences
of the extracellular domains of the immunoglobulin
superfamily. Possible correlations between conservancy and conformation (Review). Compo Biochem.
Physio1. Pt. B 80: 181-194 (1985)
9. Beck G. et a1.: Characterization of interleukin-l
activity in tunicates. Compo Biochem. Physio1. Pt. B
92: 93-98 (1989)
10. Becker R. S. and Knight K. L.: Somatic diversification of immunoglobulin heavy chain VDJ genes.
Evidence for somatic conversion in rabbits. Cell 63:
987-997 (1990)
11. Bentley D. R.: Primary structure of human complement component C2. Homology to two unrelated
protein families. Biochem. J. 239: 339-345 (1986)