A Type I Collagen Reporter Gene Construct for Protein Engineering Studies. Functional Equivalence of Transfected Reporter COL1A1 and Endogenous Gene Products During Biosynthesis and in Vitro Extracellular Matrix Accumulation

A type I collagen reporter gene construct, designed to facilitate detailed analysis of the consequences of introduced structural and regulatory mutations on collagen biosynthesis and participation in the extracellular matrix, was produced by site-directed mutagenesis of the mouse COL1A1 gene. The reporter construct, pWTCI-Ile822, carried a single base change which converted the codon for amino acid 822 of the triple helix from methionine to isoleucine. This change allowed the reporter protein, [Ile822]alpha 1(I), to be distinguished from the wild-type alpha 1(I), and quantified, by its altered CNBr cleavage pattern. In mouse Mov13 cells, which synthesize no endogenous pro alpha 1(I), reporter chains associated with endogenous pro alpha 2(I), formed pepsin-stable triple helices and were secreted efficiently from the cell. The thermal stability of wild-type molecules and molecules containing the reporter [Ile822]alpha 1(I) chains was identical. The biosynthetic characteristics of wild-type and reporter chains were directly compared in stably transfected 3T6 cells. These cells did not make a distinction between reporter and endogenous alpha 1(I) chains, which were secreted from the cells at the same rate and were processed and deposited into the 3T6 cell in vitro accumulated extracellular matrix with equal efficiency. These data demonstrate that the helical sequence alteration in the reporter protein is functionally neutral and that the reporter construct, pWTCI-Ile822, is a suitable vector for the analysis of the biochemical effects of site-directed mutations in the putative COL1A1 functional domains.