Alibardi Lorenzo, Dalla Valle Luisa, Toffolo Vania, Toni Mattia
Dipartimento di Biologia Evoluzionistica Sperimentale, University of Bologna, Bologna, Italy.
Anat Rec A Discov Mol Cell Evol Biol. 2006 Jul;288(7):734-52. doi: 10.1002/ar.a.20342.
Small proteins termed beta-keratins constitute the hard corneous material of reptilian scales. In order to study the cell site of synthesis of beta-keratin, an antiserum against a lizard beta-keratin of 15-16 kDa has been produced. The antiserum recognizes beta-cells of lizard epidermis and labels beta-keratin filaments using immunocytochemistry and immunoblotting. In situ hybridization using a cDNA-probe for a lizard beta-keratin mRNA labels beta-cells of the regenerating and embryonic epidermis of lizard. The mRNA is localized free in the cytoplasm or is associated with keratin filaments of beta-cells. The immunolabeling and in situ labeling suggest that synthesis and accumulation of beta-keratin are closely associated. Nuclear localization of the cDNA probe suggests that the primary transcript is similar to the cytoplasmic mRNA coding for the protein. The latter comprises a glycine-proline-rich protein of 15.5 kDa that contains 163 amino acids, in which the central amino acid region is similar to that of chick claw/feather while the head and tail regions resemble glycine-tyrosine-rich proteins of mammalian hairs. This is also confirmed by phylogenetic analysis comparing reptilian glycine-rich proteins with cytokeratins, hair keratin-associated proteins, and claw/feather keratins. It is suggested that different small glycine-rich proteins evolved from progenitor proteins present in basic (reptilian) amniotes. The evolution of these proteins originated glycine-rich proteins in scales, claws, beak of reptiles and birds, and in feathers. Some evidence suggests that at least some proteins contained within beta-keratin filaments are rich in glycine and resemble some keratin-associated proteins present in mammalian corneous derivatives. It is suggested that glycine-rich proteins with the chemical composition, immunological characteristics, and molecular weight of beta-keratins may represent the reptilian counterpart of keratin-associated proteins present in hairs, nails, hooves, and horns of mammals. These small proteins produce a hard type of corneous material due to their dense packing among cytokeratin filaments.
被称为β-角蛋白的小蛋白质构成了爬行动物鳞片的坚硬角质物质。为了研究β-角蛋白的合成细胞位点，制备了一种针对15 - 16 kDa蜥蜴β-角蛋白的抗血清。该抗血清可识别蜥蜴表皮的β细胞，并通过免疫细胞化学和免疫印迹标记β-角蛋白丝。使用蜥蜴β-角蛋白mRNA的cDNA探针进行原位杂交，可标记蜥蜴再生和胚胎表皮的β细胞。该mRNA定位于细胞质中游离状态或与β细胞的角蛋白丝相关联。免疫标记和原位标记表明β-角蛋白的合成与积累密切相关。cDNA探针的核定位表明初级转录本与编码该蛋白质的细胞质mRNA相似。后者是一种富含甘氨酸-脯氨酸的15.5 kDa蛋白质，包含163个氨基酸，其中央氨基酸区域与鸡爪/羽毛的相似，而头部和尾部区域类似于哺乳动物毛发中富含甘氨酸-酪氨酸的蛋白质。通过将爬行动物富含甘氨酸的蛋白质与细胞角蛋白、毛发角蛋白相关蛋白和爪/羽毛角蛋白进行系统发育分析，也证实了这一点。有人认为，不同的富含甘氨酸的小蛋白质是从基础（爬行动物）羊膜动物中存在的祖蛋白进化而来的。这些蛋白质的进化产生了爬行动物和鸟类的鳞片、爪子、喙以及羽毛中的富含甘氨酸的蛋白质。一些证据表明，β-角蛋白丝中包含的至少一些蛋白质富含甘氨酸，并且类似于哺乳动物角质衍生物中存在的一些角蛋白相关蛋白。有人认为，具有β-角蛋白的化学组成、免疫特性和分子量的富含甘氨酸的蛋白质可能代表了哺乳动物毛发、指甲、蹄和角中存在的角蛋白相关蛋白的爬行动物对应物。这些小蛋白质由于在细胞角蛋白丝之间紧密堆积而产生一种坚硬的角质物质。
