Conformational studies of the human complex-forming glycoprotein, heterogeneous in charge: protein HC

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Abstract
Human complex-forming glycoprotein, heterogeneous in charge, is a single polypeptide chain widely distributed in physiological fluids. The conformation of the protein was studied with attention to the secondary and tertiary structures. Circular dichroism and predictive methods from the amino acid sequence were employed for the characterization of the secondary structure. This is composed of 20% .alpha.-helix, 21% .beta.-structure, 29% .beta.-turns, 30% aperiodic conformation and an average number of residues per helical segment of 9. Titration of the protein indicated the existence of 2 groups for the tyrosine residues, each of them composed of 3 and 5 residues. The 4 tryptophan residues of the molecule are located in 2 different polarity microenvironments, according to the fluroescence studies. These observations are corroborated by studying the hydropathic profile of the protein. Three different domains are observed in the protein, one of them being exposed and containing the main part of the unordered structure of the molecule. The chromophore naturally associated with the protein was resolved in 3 fluorescent units not dependent on the protein conformation. These bands were observed centered around 290, 360 and 410 nm, which do not correspond to any described to any described chromophore.
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