The Staining Pattern of Collagen Fibrils: Ii. a Comparison With Patterns Computer-Generated From the Amino Acid Sequence

Abstract

The known amino acid sequence of the α1 chain of collagen enables the distribution of electric charges along the molecule to be predicted (with the assumptions that the residues, including those in the telopeptides, are uniformly spaced and that the charge distribution in the α2 chain is similar to that in the α1). By summing this distribution for a set of molecules, mutually staggered by p residues, a histogram showing the predicted distribution of charge along a fibril can be generated. Histograms constructed in this way were compared with densitometric tracings taken from electron micrographs of band patterns from collagen fibrils doubly stained with metal-containing cations and anions. This comparison was made for various values of p, and it was extended to histograms artificially smoothed in an attempt to observe histograms and tracings at comparable resolutions. In this way p, which in the fibril is the number of residues per chain contained in the period D, can be deduced from the comparison yielding the “best fit”. An objective measure of “best fit” was obtained by a correlation analysis. This analysis indicates that the number of residues in a period is p = 232.3 ± 0.5 where the error is the standard deviation obtained by statistical means. A rough confirmation of this result was made by visual comparison of a fibril banding pattern with patterns computer-generated from the sequence.