Structure analysis of fibrinogen by electron microscopy and image processing.

Abstract

Human fibrinogen was observed by electron microscopy following rotary shadowing with tungsten. Structure analysis of the molecules was performed by image processing of electron micrographs. A method is described for selection, alignment, and classification of molecules. The widely accepted overall trinodular structure of the protein was observed. The flexibility about the central domain of the molecule was quantitatively analyzed. A Gaussian distribution of this conformational parameter was obtained having an average corresponding to a maximally extended structure. Correspondence analysis applied to the aligned images showed that the degree of folding of the molecule was continuously distributed. The averaged structure of fibrinogen was estimated to be 450 A long. The central domain had a diameter of 50 A and the peripheral domains were 90 A long and 50 A wide. The latter regions had two separated maxima of scattering density.