381
harder keratinization – in the shell (see for review Dalla Valle et al. 2009a ). Some
amounts of ß-keratins are also synthetized in the soft epidermis of marine turtles
(Alibardi et al. 2004 ; Alibardi and Toni 2006 , 2007a ). In various terrestrial tortoises,
such structures as the precorneous layers of carapace and plastron epidermis, as
well as the tough scales, are responsible for synthesis of the ß-keratins (Alibardi
2002 , 2005 , 2006 ). Different forms of ß-keratins in turtles are produced from low
molecular weight precursors. Later these aggregate into larger forms during protein
preparation (Alibardi and Toni 2006 ). Interestingly, β-keratins of crocodilians and
birds origin are similar to those from turtle shell due to their glycine-proline- tyrosine
rich content (Dalla Valle et al. 2009a ; Fraser and Parry 2011 ).
Alibardi and Toni ( 2007b ) also reported about the role of keratinocites in formation of a corneous cell envelope in crocodiles, as well as about characterization of
keratins and associated proteins within crocodilian epidermis especially with
respect to its corneifi cation. These researchers showed that “some acidic alphakeratins with a weight of 47–68 kDa are present. Smaller, 17–20 kDa beta-keratins
with a prevalent basic pI (7.0–8.4) are also present. Acidic beta-keratins with a MW
of 10–16 kDa are scarce, and may represent altered forms of the original basic proteins. Crocodilian beta-keratins are not recognized by a lizard beta-keratin antibody
(A68B), and by a turtle beta-keratin antibody (A685). This result indicates that
these antibodies recognize specifi c epitopes in different reptiles. Conversely, crocodilian beta-keratins cross-react with the Beta-universal antibody indicating they
share a specifi c 20 amino acid epitope with avian beta-keratins. Although crocodilian beta-keratins are larger proteins than those present in birds, the obtained results
indicate the presence of shared epitopes between avian and crocodilian betakeratins. This is a good start for the future determination of the sequence of these
proteins,” (Alibardi and Toni 2007b ). Unfortunately, there is a lack of information
in detail on keratins from saltwater crocodile C. porosus , with exception of the
paper by Alibardi and Toni ( 2007c ).
Recently, Ye et al. ( 2010 ) showed that “beta-keratins in crocodiles reveal amino
acid homology with avian keratins. Through the deduced amino acid sequence,
these proteins are rich in glycine, proline and serine. The central region of the
proteins is composed of two beta-folded regions, and show a high degree of identity with beta-keratins of aves and squamates. This central part is thought to be the
site of polymerization to build the framework of beta-keratin fi laments. It is
believed that the beta-keratins in reptiles and birds share a common ancestry. Near
the C-terminal, these beta-keratins contain a peptide rich in glycine-X and
glycine-X- X. The distinctive feature of the region is some 12-amino acid repeats,
which are similar to the 13-amino acid repeats in chick scale keratin, but are
absent from avian feather keratin. From the phylogenetic analysis, the beta-keratins in crocodile have a closer relationship with avian keratins than the other keratins
in reptiles,” (Ye et al. 2010 ).
Principally, it is suggested that feather keratins diversifi ed early from nonfeather
keratins, deep in archosaur evolution (Dalla Valle et al. 2009b ).
11 Marine Keratins
harder keratinization – in the shell (see for review Dalla Valle et al. 2009a ). Some
amounts of ß-keratins are also synthetized in the soft epidermis of marine turtles
(Alibardi et al. 2004 ; Alibardi and Toni 2006 , 2007a ). In various terrestrial tortoises,
such structures as the precorneous layers of carapace and plastron epidermis, as
well as the tough scales, are responsible for synthesis of the ß-keratins (Alibardi
2002 , 2005 , 2006 ). Different forms of ß-keratins in turtles are produced from low
molecular weight precursors. Later these aggregate into larger forms during protein
preparation (Alibardi and Toni 2006 ). Interestingly, β-keratins of crocodilians and
birds origin are similar to those from turtle shell due to their glycine-proline- tyrosine
rich content (Dalla Valle et al. 2009a ; Fraser and Parry 2011 ).
Alibardi and Toni ( 2007b ) also reported about the role of keratinocites in formation of a corneous cell envelope in crocodiles, as well as about characterization of
keratins and associated proteins within crocodilian epidermis especially with
respect to its corneifi cation. These researchers showed that “some acidic alphakeratins with a weight of 47–68 kDa are present. Smaller, 17–20 kDa beta-keratins
with a prevalent basic pI (7.0–8.4) are also present. Acidic beta-keratins with a MW
of 10–16 kDa are scarce, and may represent altered forms of the original basic proteins. Crocodilian beta-keratins are not recognized by a lizard beta-keratin antibody
(A68B), and by a turtle beta-keratin antibody (A685). This result indicates that
these antibodies recognize specifi c epitopes in different reptiles. Conversely, crocodilian beta-keratins cross-react with the Beta-universal antibody indicating they
share a specifi c 20 amino acid epitope with avian beta-keratins. Although crocodilian beta-keratins are larger proteins than those present in birds, the obtained results
indicate the presence of shared epitopes between avian and crocodilian betakeratins. This is a good start for the future determination of the sequence of these
proteins,” (Alibardi and Toni 2007b ). Unfortunately, there is a lack of information
in detail on keratins from saltwater crocodile C. porosus , with exception of the
paper by Alibardi and Toni ( 2007c ).
Recently, Ye et al. ( 2010 ) showed that “beta-keratins in crocodiles reveal amino
acid homology with avian keratins. Through the deduced amino acid sequence,
these proteins are rich in glycine, proline and serine. The central region of the
proteins is composed of two beta-folded regions, and show a high degree of identity with beta-keratins of aves and squamates. This central part is thought to be the
site of polymerization to build the framework of beta-keratin fi laments. It is
believed that the beta-keratins in reptiles and birds share a common ancestry. Near
the C-terminal, these beta-keratins contain a peptide rich in glycine-X and
glycine-X- X. The distinctive feature of the region is some 12-amino acid repeats,
which are similar to the 13-amino acid repeats in chick scale keratin, but are
absent from avian feather keratin. From the phylogenetic analysis, the beta-keratins in crocodile have a closer relationship with avian keratins than the other keratins
in reptiles,” (Ye et al. 2010 ).
Principally, it is suggested that feather keratins diversifi ed early from nonfeather
keratins, deep in archosaur evolution (Dalla Valle et al. 2009b ).
11 Marine Keratins