Origin and Mechanism of Evolution of Antifreeze Glycoproteins in Polar Fishes
321
frame for three temporally related events - freezing of the Antarctic water,
evolution of notothenioid AFGP gene, and speciation and radiation of
notothenioid fishes. It is difficult to dismiss such remarkable agreement as
mere coincidence. Indeed this is a rare case in which protein evolution,
organismal adaptation, and environment conditions can be linked directly
through corroborating biological/molecular and physical evidence.
Innovativeness of the Evolutionary Process of Notothenioid
AFGP Gene
The evolutionary process by which notothenioid AFGP genes arose is
novel and creative. Most new genes evolve from existing genes or gene
segments, either through duplication and divergence [40], recruitment [41]
or exon shuffling [42]. Type II AFPs of sea raven, smelt and herring, the
only other antifreeze protein with a known evolutionary origin - the
carbohydrate binding domain of C-type lectins [19] - apparently arose
through straight forward duplication and divergence. The formation of the
notothenioid AFGP gene indeed utilized some aspects of these known
mechanisms. What sets it apart is that an entire new protein coding region
was built up from a rudimentary foundation - a minimal partly noncoding
(A)
• Signal peptide D AFGP isoforms I spacer
start
stop
5' m 11 1-u1111111111111111 1 I I I 71 I I I I 13 E:i"~~ 3'
E1
E2
E3
(B)
Trypsin-like protease
------ I
d I- -
~
[~~~~
-----I
Carboxypeptidase
J
I~
...
l
tRI
IR I
IRAARI
~
AFGP molecules
I I
IRAA I
I I
Fig. 4. A Structure of an AFGP polyprotein gene from the Arctic cod Boreogadus saida
(clone Bs3L, [30]) that will produce 13 molecules of AFGP if all the spacers (Arg residues)
are cleaved. B Processing of the AFGP polyprotein precursor. A trypsin-like protease
cleaves at the carboxyl side of Arg (R), and a carboxypeptidase removes the Arg, producing
the individual mature AFGPs. Not all spacers are removed as a small percentage of Arg is
retained in the mature AFGPs
321
frame for three temporally related events - freezing of the Antarctic water,
evolution of notothenioid AFGP gene, and speciation and radiation of
notothenioid fishes. It is difficult to dismiss such remarkable agreement as
mere coincidence. Indeed this is a rare case in which protein evolution,
organismal adaptation, and environment conditions can be linked directly
through corroborating biological/molecular and physical evidence.
Innovativeness of the Evolutionary Process of Notothenioid
AFGP Gene
The evolutionary process by which notothenioid AFGP genes arose is
novel and creative. Most new genes evolve from existing genes or gene
segments, either through duplication and divergence [40], recruitment [41]
or exon shuffling [42]. Type II AFPs of sea raven, smelt and herring, the
only other antifreeze protein with a known evolutionary origin - the
carbohydrate binding domain of C-type lectins [19] - apparently arose
through straight forward duplication and divergence. The formation of the
notothenioid AFGP gene indeed utilized some aspects of these known
mechanisms. What sets it apart is that an entire new protein coding region
was built up from a rudimentary foundation - a minimal partly noncoding
(A)
• Signal peptide D AFGP isoforms I spacer
start
stop
5' m 11 1-u1111111111111111 1 I I I 71 I I I I 13 E:i"~~ 3'
E1
E2
E3
(B)
Trypsin-like protease
------ I
d I- -
~
[~~~~
-----I
Carboxypeptidase
J
I~
...
l
tRI
IR I
IRAARI
~
AFGP molecules
I I
IRAA I
I I
Fig. 4. A Structure of an AFGP polyprotein gene from the Arctic cod Boreogadus saida
(clone Bs3L, [30]) that will produce 13 molecules of AFGP if all the spacers (Arg residues)
are cleaved. B Processing of the AFGP polyprotein precursor. A trypsin-like protease
cleaves at the carboxyl side of Arg (R), and a carboxypeptidase removes the Arg, producing
the individual mature AFGPs. Not all spacers are removed as a small percentage of Arg is
retained in the mature AFGPs