The & crystallin of the ostrich Struthio camelus
also has high arginine succinate lyase activity
[40,310]. E Crystallin was discovered in the Peking duck but also occurs in other avian species,
e.g. vultures and stilts, in proportions of up to
23 % of the lens protein; it is not found in the
chicken. It is also present in the eye lenses of crocodiles but does not occur in any other reptiles. E
Crystallin is homologous to the heart-specific
isoenzyme B4 of lactate dehydrogenase (LDHB4)' Ducks and chickens possess only one LDH-B
gene which codes for both E crystallin and the cell
enzyme. Thus, the gene product in this case must
be adapted to two quite different functions and
this "gene sharing" results in a radically reduced
rate of evolution. Like LDH-B4' E crystallin is a
homotetramer and differs from the cell enzyme
only by the deamidation of the asparagine residues in positions 163 and 265 [99].
Taxon-specific crystaIlins have only quite
recently been discovered in the mammals; the
first to be found was f... crystallin, which makes up
about 7-8 % of the soluble protein in the lenses
of rabbits and hares and shows 30 % sequence
agreement with L-3-hydroxacyl-CoA-dehydrogenase from mitochondria [197]. The ~ crystallin
from the lens of the quinea-pig Cavia poceUus
belongs to the family of zinc-containing longchained alcohol/polyol dehydrogenases. However,
adaptation to the function of lens protein has led
not only to the loss of the zinc-binding amino
acids, and therefore loss of the enzyme activity
during evolution, but also to other changes. Thus,
the lens protein is tetrameric, like mammalian sorbitol dehydrogenase, and not dimeric, like the
zinc-containing alcohol dehydrogenases. Surprisingly, ~ crystallin is found not only in the guineapig and other hystricomorphs but also in Camelus
dromedarius, a representative of a different mammalian order [77]. The eye lenses of three species
of the primitive elephant shrews (Macroscleidae)
have been shown to contain up to 24 % soluble 1]
crystallin, which is apparently identical to cytosolic
aldehyde oxidase. However, the lens shows no
enzyme activity, probably as the result of ageing
processes [312]. In the tammar wallaby Macropus
eugenii and the tiger cat Dasyurops maculatus
(Marsupalia), the lens contains a !l crystallin which
appears to have a nucleotide-binding structure but
has no homology to known dehydrogenases [312].
The Q crystallin isolated from the lenses of
Rana temporaria and R. catesbeiana shows high
sequence homology to aldehyde reductase, aldose
reductase and prostaglandin-F synthase. The frog
lens contains an N-terminal acylated (RHO-I) and
References
367
a non-blocked (RHO-II) form of the lens protein,
neither of which has enzyme activity [75]. The aenolase-homologous 1: crystallin is found in the
lamprey and also in certain species of birds, reptiles and teleosts. The duck has only one a-enolaseh
crystallin gene, which thus codes for a protein with
two different functions. However, the enzyme
activity in the lens is reduced by ageing processes
[120].
The invertebrates have no crystallins, not even
the cephalopods, whose eyes are so similar to
those of the vertebrates as to serve as a remarkable example of convergent evolution. The lenses
of cephalopod eyes contain an electrophoretically
complex spectrum of proteins which are, however,
also termed crystallins. The main lens proteins of
Ommastrephes sloani are homo- or heterodimers,
with subunits of 222-223 amino acids, encoded by
a gene family with at least three members. Two of
these genes show only 50 % agreement in their
amino acid sequences but both are significantly
homologous to rat glutathione-S-transferase.
Similar lens proteins have been detected in Octopus vulgaris and Sepia esculenta, which belong to
very different cephalopod groups [38, 284].
References
1. Aarts H. J. M., Lubsen N. H. and Schoenmakers J. G.
G.: Crystallin gene expression during rat lens development. Eur. J. Biochem. 183: 31-36 (1989)
2. Abe H. et al.: Sequence of cDNAs encoding actin
depolymerizing factor and cofilin of embryonic
chicken skeletal muscle: Two functionally distinct
actin-regulatory proteins exhibit high structural homology. Biochemistry 29: 7420-25 (1990)
3. Alonso S. et al.: Comparison of three actin-coding
sequences in the mouse: evolutionary relationships
between actin genes of warm-blooded vertebrates. J.
mol. Evol. 23: 11-22 (1986)
4. Ampe C. et al.: The primary structure of the basic isoform of Acanthamoeba profilin. Eur. J. Biochem. 170:
597-601 (1988)
5. Anderson P.: Molecular genetics of nematode muscle.
Annual Rev. Genet. 23: 507-525 (1989)
6. Arimura C. et al.: Primary structure of chicken skeletal
muscle and fibroblast a-actinins deduced from cDNA
sequences. Eur. J. Biochem. 177: 649-655 (1988)
7. Baba M. L. et al.: The early adaptive evolution of calmodulin. Mol. BioI. Evol. 1: 442-455 (1984)
8. Babu Y. S. et al.: Three-dimensional structure of calmodulin. Nature 315: 37-40 (1985)
9. Balcarek J. M. and Cowan N. J.: Structure of the
mouse glial fibrillary acidic protein gene: implications
for the evolution of the intermediate filament multigene family. Nucleic Acids Res. 13: 5527-43 (1985)
10. Ball E. et al.: Arthrin, a myofibrillar protein of insect
flight muscle, is an actin-ubiquitin conjugate. Cell 51:
221-228 (1987)
also has high arginine succinate lyase activity
[40,310]. E Crystallin was discovered in the Peking duck but also occurs in other avian species,
e.g. vultures and stilts, in proportions of up to
23 % of the lens protein; it is not found in the
chicken. It is also present in the eye lenses of crocodiles but does not occur in any other reptiles. E
Crystallin is homologous to the heart-specific
isoenzyme B4 of lactate dehydrogenase (LDHB4)' Ducks and chickens possess only one LDH-B
gene which codes for both E crystallin and the cell
enzyme. Thus, the gene product in this case must
be adapted to two quite different functions and
this "gene sharing" results in a radically reduced
rate of evolution. Like LDH-B4' E crystallin is a
homotetramer and differs from the cell enzyme
only by the deamidation of the asparagine residues in positions 163 and 265 [99].
Taxon-specific crystaIlins have only quite
recently been discovered in the mammals; the
first to be found was f... crystallin, which makes up
about 7-8 % of the soluble protein in the lenses
of rabbits and hares and shows 30 % sequence
agreement with L-3-hydroxacyl-CoA-dehydrogenase from mitochondria [197]. The ~ crystallin
from the lens of the quinea-pig Cavia poceUus
belongs to the family of zinc-containing longchained alcohol/polyol dehydrogenases. However,
adaptation to the function of lens protein has led
not only to the loss of the zinc-binding amino
acids, and therefore loss of the enzyme activity
during evolution, but also to other changes. Thus,
the lens protein is tetrameric, like mammalian sorbitol dehydrogenase, and not dimeric, like the
zinc-containing alcohol dehydrogenases. Surprisingly, ~ crystallin is found not only in the guineapig and other hystricomorphs but also in Camelus
dromedarius, a representative of a different mammalian order [77]. The eye lenses of three species
of the primitive elephant shrews (Macroscleidae)
have been shown to contain up to 24 % soluble 1]
crystallin, which is apparently identical to cytosolic
aldehyde oxidase. However, the lens shows no
enzyme activity, probably as the result of ageing
processes [312]. In the tammar wallaby Macropus
eugenii and the tiger cat Dasyurops maculatus
(Marsupalia), the lens contains a !l crystallin which
appears to have a nucleotide-binding structure but
has no homology to known dehydrogenases [312].
The Q crystallin isolated from the lenses of
Rana temporaria and R. catesbeiana shows high
sequence homology to aldehyde reductase, aldose
reductase and prostaglandin-F synthase. The frog
lens contains an N-terminal acylated (RHO-I) and
References
367
a non-blocked (RHO-II) form of the lens protein,
neither of which has enzyme activity [75]. The aenolase-homologous 1: crystallin is found in the
lamprey and also in certain species of birds, reptiles and teleosts. The duck has only one a-enolaseh
crystallin gene, which thus codes for a protein with
two different functions. However, the enzyme
activity in the lens is reduced by ageing processes
[120].
The invertebrates have no crystallins, not even
the cephalopods, whose eyes are so similar to
those of the vertebrates as to serve as a remarkable example of convergent evolution. The lenses
of cephalopod eyes contain an electrophoretically
complex spectrum of proteins which are, however,
also termed crystallins. The main lens proteins of
Ommastrephes sloani are homo- or heterodimers,
with subunits of 222-223 amino acids, encoded by
a gene family with at least three members. Two of
these genes show only 50 % agreement in their
amino acid sequences but both are significantly
homologous to rat glutathione-S-transferase.
Similar lens proteins have been detected in Octopus vulgaris and Sepia esculenta, which belong to
very different cephalopod groups [38, 284].
References
1. Aarts H. J. M., Lubsen N. H. and Schoenmakers J. G.
G.: Crystallin gene expression during rat lens development. Eur. J. Biochem. 183: 31-36 (1989)
2. Abe H. et al.: Sequence of cDNAs encoding actin
depolymerizing factor and cofilin of embryonic
chicken skeletal muscle: Two functionally distinct
actin-regulatory proteins exhibit high structural homology. Biochemistry 29: 7420-25 (1990)
3. Alonso S. et al.: Comparison of three actin-coding
sequences in the mouse: evolutionary relationships
between actin genes of warm-blooded vertebrates. J.
mol. Evol. 23: 11-22 (1986)
4. Ampe C. et al.: The primary structure of the basic isoform of Acanthamoeba profilin. Eur. J. Biochem. 170:
597-601 (1988)
5. Anderson P.: Molecular genetics of nematode muscle.
Annual Rev. Genet. 23: 507-525 (1989)
6. Arimura C. et al.: Primary structure of chicken skeletal
muscle and fibroblast a-actinins deduced from cDNA
sequences. Eur. J. Biochem. 177: 649-655 (1988)
7. Baba M. L. et al.: The early adaptive evolution of calmodulin. Mol. BioI. Evol. 1: 442-455 (1984)
8. Babu Y. S. et al.: Three-dimensional structure of calmodulin. Nature 315: 37-40 (1985)
9. Balcarek J. M. and Cowan N. J.: Structure of the
mouse glial fibrillary acidic protein gene: implications
for the evolution of the intermediate filament multigene family. Nucleic Acids Res. 13: 5527-43 (1985)
10. Ball E. et al.: Arthrin, a myofibrillar protein of insect
flight muscle, is an actin-ubiquitin conjugate. Cell 51:
221-228 (1987)