Immunocytochemistry and protein analysis suggest that reptilian claws contain small high cysteine-glycine proteins.
The present study analyzes the structure and the main proteins of reptilian claws. Mature claws are formed by two to four layers of keratinocytes, a transitional layer of spindle-shaped cells and a thick corneous layer. Transitional cells elongate and merge into a compact corneous layer that is immunoreactive for beta-keratins, now indicated as sauropsid keratin-associated proteins (sKAPs). Most proteins extracted from claws in representative reptiles have a molecular weight of 13-20kDa, an acidic to basic isoelectric point, and are identified from the positive immunoreactivity to beta-keratin antibodies. The comparative analysis between lizard and avian claw beta-keratins shows the presence of an internal region of 20 amino acids with the highest identity, indicated as core-box, within an extended 32-amino acid region with a prevalent beta-sheet secondary conformation. This region is structurally equivalent to a 32-amino acid region present in scale beta-keratins of most reptiles. Both reptilian and avian keratins contain glycine-rich regions for stabilization of the beta-keratin polymer. The N- and C-regions contain most cysteine for disulphide-bonds formation. Claw proteins contain higher amount of cysteine and glycine than other scale proteins, suggesting that claw proteins are specialized cysteine-glycine-rich proteins suited to produce a very hard corneous material.
Alibardi
L
L
Dipartimento di Biologia evoluzionistica sperimentale, University of Bologna, 40126, Bologna, Italy. lorenzo.alibardi@unibo.it
Toni
M
M
D000489:Alligators and Crocodiles / Q000033:anatomy & histology / Q000378:metabolism; D000595:Amino Acid Sequence / Q000502:physiology; D000818:Animals; D017124:Conserved Sequence / Q000235:genetics; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D019143:Evolution, Molecular; D005998:Glycine / Q000737:chemistry / Q000378:metabolism*; D006724:Hoof and Claw / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D008116:Lizards / Q000033:anatomy & histology / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary / Q000502:physiology; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D040901:Proteomics / Q000379:methods; D012104:Reptiles / Q000033:anatomy & histology / Q000378:metabolism*; D013045:Species Specificity; D014426:Turtles / Q000033:anatomy & histology / Q000378:metabolism
D011506:Proteins; D003545:Cysteine; D005998:Glycine