Bonadio J, Holbrook K A, Gelinas R E, Jacob J, Byers P H
J Biol Chem. 1985 Feb 10;260(3):1734-42.
Cultured dermal fibroblasts from an infant with the lethal perinatal form of osteogenesis imperfecta (type II) synthesize normal and abnormal forms of type I procollagen. The abnormal type I procollagen molecules are excessively modified during their intracellular stay, have a lower than normal melting transition temperature, are secreted at a reduced rate, and form abnormally thin collagen fibrils in the extracellular matrix in vitro. Overmodification of the abnormal type I procollagen molecules was limited to the NH2-terminal three-fourths of the triple helical domain. Two-dimensional mapping of modified and unmodified alpha chains of type I collagen demonstrated neither charge alterations nor large insertions or deletions in the region of alpha 1(I) and alpha 2(I) in which overmodification begins. Both the structure and function of type I procollagen synthesized by cells from the parents of this infant were normal. The simplest interpretation of the results of this study is that the osteogenesis imperfecta phenotype arose from a new dominant mutation in one of the genes encoding the chains of type I procollagen. Given the requirement for glycine in every third position of the triple helical domain, the mutation may represent a single amino acid substitution for a glycine residue. These findings demonstrate further heterogeneity in the biochemical basis of osteogenesis imperfecta type II and suggest that the nature and location of mutations in type I procollagen may determine phenotypic variation.
来自一名患有致死性围产期成骨不全（II型）婴儿的培养皮肤成纤维细胞能合成正常和异常形式的I型前胶原。异常的I型前胶原分子在细胞内停留期间被过度修饰，具有低于正常的解链转变温度，分泌速率降低，并且在体外细胞外基质中形成异常细的胶原纤维。异常I型前胶原分子的过度修饰仅限于三螺旋结构域的NH2末端四分之三部分。I型胶原修饰和未修饰α链的二维图谱显示，在过度修饰开始的α1（I）和α2（I）区域，既没有电荷改变，也没有大的插入或缺失。该婴儿父母的细胞合成的I型前胶原的结构和功能均正常。这项研究结果最简单的解释是，成骨不全表型源于编码I型前胶原链的基因之一的新显性突变。鉴于三螺旋结构域每隔三个位置就需要甘氨酸，该突变可能代表一个甘氨酸残基被单个氨基酸取代。这些发现进一步证明了II型成骨不全生化基础的异质性，并表明I型前胶原突变的性质和位置可能决定表型变异。
