Grobe K, Becker W M, Schlaak M, Petersen A
University of California, La Jolla, CA, USA.
Eur J Biochem. 1999 Jul;263(1):33-40. doi: 10.1046/j.1432-1327.1999.00462.x.
Expansins are a family of proteins that catalyse long-term extension of isolated plant cell walls due to an as yet unknown biochemical mechanism. They are divided into two groups, the alpha-expansins and beta-expansins, the latter group consisting of grass group I allergens and their vegetative homologs. These grass group I allergens, to which more than 95% of patients allergic to grass pollen possess IgE antibodies, are highly immunologically crossreactive glycoproteins exclusively expressed in pollen of all grasses. Alignments of the amino-acid sequences of grass group I allergens derived from diverse grass species reveal up to 95% homology. It is therefore likely that these molecules share a similar biological function. The major grass group I allergen from timothy grass (Phleum pratense), Phl p 1, was chosen as a model glycoprotein and expressed in the methylotrophic yeast Pichia pastoris to obtain a post-translationally modified and functionally active allergen. The recombinant allergen exhibited proteolytic activity when assayed with various test systems and substrates, which was also subsequently demonstrated with the natural protein, nPhl p 1. These observations are confirmed by amino-acid alignments of Phl p 1 with three functionally important sequence motifs surrounding the active-site amino acids of the C1 (papain-like) family of cysteine proteinases. Moreover, the significantly homologous alpha-expansins mostly share the functionally important C1 sequence motifs. This leads us to propose a C1 cysteine proteinase function for grass group I allergens, which may mediate plant cell wall growth and possibly contributes to the allergenicity of the molecule.
扩展蛋白是一类蛋白质，它们通过一种尚未明确的生化机制催化离体植物细胞壁的长期伸展。它们分为两组，即α-扩展蛋白和β-扩展蛋白，后者由禾本科I组过敏原及其营养同源物组成。超过95%对禾本科花粉过敏的患者对这些禾本科I组过敏原具有IgE抗体，它们是高度免疫交叉反应的糖蛋白，仅在所有禾本科植物的花粉中表达。对来自不同禾本科物种的禾本科I组过敏原的氨基酸序列进行比对，发现同源性高达95%。因此，这些分子可能具有相似的生物学功能。选择来自梯牧草（Phleum pratense）的主要禾本科I组过敏原Phl p 1作为模型糖蛋白，并在甲基营养酵母毕赤酵母中表达，以获得翻译后修饰且功能活跃的过敏原。用各种测试系统和底物检测时，重组过敏原表现出蛋白水解活性，天然蛋白nPhl p 1随后也证实了这一点。通过将Phl p 1与半胱氨酸蛋白酶C1（木瓜蛋白酶样）家族活性位点氨基酸周围的三个功能重要序列基序进行氨基酸比对，证实了这些观察结果。此外，显著同源的α-扩展蛋白大多共享功能重要的C1序列基序。这使我们提出禾本科I组过敏原具有C1半胱氨酸蛋白酶功能，该功能可能介导植物细胞壁生长，并可能导致该分子具有过敏原性。
