Molhuizen H O, Alkemade H A, Zeeuwen P L, de Jongh G J, Wieringa B, Schalkwijk J
Department of Dermatology, Academic Hospital, Nijmegen, The Netherlands.
J Biol Chem. 1993 Jun 5;268(16):12028-32.
SKALP/Elafin is a proteinase inhibitor found in psoriatic epidermis as a short polypeptide of 6 kDa. Here we present evidence that this protein is synthesized as a larger precursor molecule with distinct biological features. Purification and NH2-terminal sequencing of SKALP/elafin from cultured human keratinocytes and the cloning of its cDNA revealed the existence of a mature protein, which upon cleavage of a hydrophobic signal sequence of 22 amino acids has a calculated molecular mass of 9.9 kDa (95 amino acids). In addition to the known proteinase inhibitor domain, the mature protein contains a domain with 4 repeats which are homologous to putative transglutaminase substrate motifs. We were able to demonstrate on Western blots that immunoreactive SKALP is present in high molecular weight proteins extracted from psoriatic skin. This suggests that SKALP is covalently attached to epidermal proteins. In addition it was found that both the complete SKALP molecule and a synthetic peptide of the NH2-terminal portion of SKALP could be used as a transglutaminase substrate. We therefore speculate that SKALP/elafin, secreted by epidermal keratinocytes in inflamed skin, exists both as a free 6-kDa form and as an immobilized 9.9-kDa form covalently attached to the cornified envelopes by transglutaminase cross-linking.
SKALP/Elafin是一种在银屑病表皮中发现的蛋白酶抑制剂，呈6 kDa的短多肽形式。在此我们提供证据表明，这种蛋白质是以具有独特生物学特性的更大前体分子形式合成的。从培养的人角质形成细胞中纯化SKALP/elafin并进行氨基末端测序，以及对其cDNA进行克隆，结果显示存在一种成熟蛋白质，该蛋白质在切割掉22个氨基酸的疏水信号序列后，计算分子量为9.9 kDa（95个氨基酸）。除了已知的蛋白酶抑制剂结构域外，成熟蛋白质还包含一个具有4个重复序列的结构域，这些重复序列与假定的转谷氨酰胺酶底物基序同源。我们能够在蛋白质印迹法中证明，免疫反应性SKALP存在于从银屑病皮肤中提取的高分子量蛋白质中。这表明SKALP与表皮蛋白共价连接。此外，还发现完整的SKALP分子和SKALP氨基末端部分的合成肽都可以用作转谷氨酰胺酶的底物。因此我们推测，在炎症皮肤中由表皮角质形成细胞分泌的SKALP/elafin，既以游离的6 kDa形式存在，也以通过转谷氨酰胺酶交联共价连接到角质包膜上的固定化9.9 kDa形式存在。
