Immunolocalization of Keratin‐Associated Beta‐Proteins (Beta‐Keratins) in Pad Lamellae of Geckos Suggest that Glycine–Cysteine‐Rich Proteins Contribute to Their Flexibility and Adhesiveness

Abstract

The epidermis of digital pads in geckos comprises superficial microornamentation from the oberhautchen layer that form long setae allowing these lizards to climb vertical surfaces. The beta-layer is reduced in pad lamellae but persists up to the apical free margin. Setae are made of different proteins including keratin-associated beta-proteins, formerly indicated as beta-keratins. In order to identify specific setal proteins the present ultrastructural study on geckos pad lamellae analyzes the immunolocalization of three beta-proteins previously found in the epidermis and adhesive setae of the green anolis. A protein rich in glycine but poor in cysteine (HgG5-like) is absent or masked in gecko pad lamellae. Another protein rich in glycine and cysteine (HgGC3-like) is weakly present in setae, oberhautchen and beta-layer. A glycine and cysteine medium rich beta-protein (HgGC10-like) is present in the lower part of the beta-layer but is absent in the oberhautchen, setae, and mesos layer. The latter two proteins may form intermolecular bonds that contribute to the flexibility of the corneous material sustaining the setae. The pliable alpha-layer present beneath the thin beta-layer and in the hinge region of the pad lamellae also contains HgGC10-like proteins. Based on the possibility that some HgGC3-like or other cys-rich beta-proteins are charged in the setae it is suggested that their charges influence the mechanism of adhesion increasing the induction of dipoles on the substrate and enhancing attractive van der Waals forces.