Funderburgh J L, Corpuz L M, Roth M R, Funderburgh M L, Tasheva E S, Conrad G W
Division of Biology, Kansas State University, Manhattan, Kansas 66506-4901, USA.
J Biol Chem. 1997 Oct 31;272(44):28089-95. doi: 10.1074/jbc.272.44.28089.
Bovine cornea contains three unique keratan sulfate proteoglycans (KSPGs), of which two (lumican and keratocan) have been characterized using molecular cloning. The gene for the third protein (KSPG25) has not been identified. This study examined the relationship between the KSPG25 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein. The N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea. The osteoglycin amino acid sequence makes up the C-terminal 47% of the deduced sequence of the KSPG25 protein. Antibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratocan. KSPG25-related proteins, not modified with keratan sulfate, were also detected in several connective tissues. Northern blot analysis showed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues. Ribonuclease protection analysis detected several protected KSPG25 mRNA fragments, suggesting alternate splicing of KSPG25 transcripts. We conclude that the full-length translation product of the gene producing osteoglycin is a corneal keratan sulfate proteoglycan, also present in many non-corneal tissues without keratan sulfate chains. The multiple size protein products of this gene appear to result from in situ proteolytic processing and/or alternative splicing of mRNA. The name mimecan is proposed for this gene and its products.
牛角膜含有三种独特的硫酸角质素蛋白聚糖（KSPG），其中两种（光蛋白聚糖和角膜蛋白聚糖）已通过分子克隆进行了表征。第三种蛋白质（KSPG25）的基因尚未确定。本研究探讨了KSPG25蛋白与骨甘蛋白（一种12 kDa的骨糖蛋白）基因之间的关系。KSPG25的N端氨基酸序列出现在从牛角膜克隆的骨甘蛋白cDNA中。骨甘蛋白氨基酸序列构成了KSPG25蛋白推导序列的C端47%。抗骨甘蛋白抗体与完整的角膜KSPG、KSPG25蛋白以及一种与光蛋白聚糖和角膜蛋白聚糖不同的36 kDa蛋白发生反应。在几种结缔组织中也检测到了未被硫酸角质素修饰的KSPG25相关蛋白。Northern印迹分析显示，在许多组织中存在2.4、2.5和2.6千碱基的mRNA转录本，其中2.4千碱基的转录本在眼组织中富集。核糖核酸酶保护分析检测到几个受保护的KSPG25 mRNA片段，提示KSPG25转录本存在可变剪接。我们得出结论，产生骨甘蛋白的基因的全长翻译产物是一种角膜硫酸角质素蛋白聚糖，也存在于许多没有硫酸角质素链的非角膜组织中。该基因的多种大小的蛋白质产物似乎是由mRNA的原位蛋白水解加工和/或可变剪接产生的。建议将该基因及其产物命名为mimecan。
