RESUMEN
Type I procollagen secreted by dermal fibroblasts from an individual with osteogenesis imperfecta type IV was a mixture of normal molecules and molecules that were post-translationally overmodified. The individual was heterozygous for a G to A transition in the COL1A1 gene that resulted in the substitution of serine for glycine 883 in one or both of the pro alpha 1 (I) chains. The thermal stability of molecules containing overmodified chains was lower by 2 degrees C than that of normal molecules. However, following cleavage of the molecules with vertebrate collagenase, the temperature of denaturation of the overmodified A fragments (residues 1-775 of the helix did not contain the substitution) was 2 degrees C greater than that of A fragments from normal molecules. The rates of cleavage by procollogen N-proteinase (EC 3.4.214.14) (N-proteinase) of procollagen molecules in normal and osteogenesis imperfecta samples were not significantly different. The procollagen molecules in the osteogenesis imperfecta sample were also indistinguishable from those in control samples by rotary shadowing electron microscopy. The results suggest that this substitution of serine for glycine in the alpha 1 (I) chain of procollagen, like the substitution of aspartate for the same glycine previously described (Lightfoot, S. J., Holmes, D. F., Brass, A., Grant, M. E., Byers, P. H., and Kadler, K. E. (1992) J. Biol. Chem. 267, 25521-25528), can alter the structure of the triple helix N-terminal to the site of the substitution. However, in contrast to the aspartate for glycine substitution, the structural change is insufficient to delay the cleavage of the procollagen by N-proteinase and results in a mild rather than lethal phenotype.
Asunto(s)
Glicina , Osteogénesis Imperfecta/genética , Mutación Puntual , Procolágeno N-Endopeptidasa/metabolismo , Procolágeno/química , Procolágeno/genética , Estructura Secundaria de Proteína , Secuencia de Aminoácidos , Secuencia de Bases , Preescolar , Cartilla de ADN , ADN Complementario/química , Electroforesis en Gel de Poliacrilamida , Femenino , Humanos , Cinética , Masculino , Datos de Secuencia Molecular , Osteogénesis Imperfecta/clasificación , Linaje , Fragmentos de Péptidos/química , Fragmentos de Péptidos/aislamiento & purificación , Reacción en Cadena de la Polimerasa , Procolágeno/biosíntesis , Especificidad por SustratoRESUMEN
We report the cDNA sequence for the bovine gene for fibrillin corresponding to the human gene, fibrillin 1 (FBN1), and the localization of the gene to bovine chromosome 10 (syntenic group U5). The identity between the human and bovine sequences is 97.8% at the amino acid level and 92% at the nucleotide level. The bovine fibrillin sequence contains the same number and type of motifs as the human FBN1 sequence, including the same number of putative calcium binding sites. All of the motifs conform to the patterns demonstrated in the human sequence, and many of the differences in identity between the sequences are conservative.