Morphological and conformational studies of Tamm-Horsfall urinary glycoprotein

Abstract

We have studied the circular dichroic properties of normal and cystic fibrotic Tamm-Horsfall urinary glycoproteins, and the asialo-derivatives (ca. 80% removal of sialic acid with neuraminidase). There was no evidence of α-helicity in Tamm-Horsfall urinary glycoprotein, but the results do indicate a significant amount of β-structure. The circular dichroic spectra of normal and cystic fibrotic Tamm-Horsfall urinary glycoproteins and the asialo-derivatives were identical, thus suggesting that there is no major difference in the ordered secondary structure of Tamm-Horsfall urinary glycoprotein in cystic fibrosis (relative to normal Tamm-Horsfall urinary glycoprotein), and that sialic acid exerts no major effect on the β-structure. Also, the circular dichroic spectrum of Tamm-Horsfall urinary glycoprotein was not affected by Ca 2+ at concentrations just below that required for gel formation. Electron microscopic studies reveal the presence of a supramolecular helical structure arising from subunit interactions. This structure was characterized by a repeat of 120–130 Å and a minimal helix diameter of ca. 40 Å, although this value varied depending on the number of interacting helices. The helical structure was observed for normal, cystic fibrotic, and asialo derivatives of Tamm-Horsfall urinary glycoproteins, and was independent of added Ca 2+. Guanidine hydrochloride treatment, followed by dialysis, irreversibly destroyed this supra-molecular helical structure, but the β-structure was partially restored, as indicated by the circular dichroic spectrum. The Ca 2+-mediated gel formation was found to be inhibited in asialo-Tamm-Horsfall urinary glycoprotein.