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Chi-Hing C. Cheng
groups evolved their AFGPs separately, but it is equally difficult to
conceive how two near-identical sets of complex proteins could arise
independently by chance. As gene sequences are records of evolutionary
histories, through detailed comparative analyses of the AFGP genes of
Antarctic notothenioids and northern cods, we have recently unveiled part
of the evolutionary mystery of the AFGPs [29-31].
AFGP Genes of Antarctic Notothenioids
Notothenioid AFGPs are encoded by a family of many member genes [12].
The first AFGP gene reported was from Notothenia coriiceps [32]; the
sequence was later determined to be missing the signal peptide coding
sequence [29]. We have now reported the complete sequences of two
AFGP genes from a related nototheniid, the giant Antarctic toothfish D.
mawsoni [29,30]. A diagrammatic representation of a Dm (D. mawsoni)
(A)
Signal peptide
D AFGP8 ~ AFGP7 m AFGPS spacer
5
(B)
Cbymotrypsin-Iike protea e
::::::.0.-1 _---'IL'IF'. L I r-===~::! ~ __ __»OOC' ..... 'L I _ _ _'= I~NF'1r- 1 ----rl ~~~:~:
I
Ca rbOxlpeptid ase
,----. . . . . .
(F 1
(L "'-1 -~rL
+
AFGP molecules
'---------'1 1
1 "' -1- --'
Fig. 1. A Structure of an AFGP polyprotein gene from D. mawsoni (clone Dm I A, [29]) that
encodes 41 molecules of AFGP. B Processing of the AFGP polyprotein precursor. A
chymotrypsin-like protease cleaves at Leu (L) and Phe (F), and a carboxypeptidase removes
the C-terrninus Leu or Phe, producing the individual mature AFGPs