Calcium-induced changes in chondroitin sulfate chains of urinary trypsin inhibitor

Abstract

Urinary trypsin inhibitor (UTI) has several roles other than protease inhibition. It is suggested that UTI inhibits calcium influx in cultured cells and that the chondroitin sulfate chain of UTI may play an important role. In order to clarify the mechanistic features of this phenomenon, the chondroitin sulfate chain of UTI was analyzed by 1H-NMR. The samples were highly purified UTI dissolved in D2O in the presence or absence of Ca2+, Mg2+ and Na+. 1D-spectra were obtained and T1 values of detected signals were estimated from the inversion-recovery method. The addition of Ca2+ to UTI caused a chemical shift to downfield, line broadening and a reduction of T1 values at several signals from chondroitin sulfate moiety (especially at axial H-2 of GalNAc), whereas Mg2+ and Na+ had no significant effect. Some of the signals in the linkage region of chondroitin sulfate chain showed marked line broadening by Ca2+. The reduction of T1 values implies formation of a complex. It is suggested that Ca2+ generates the sulfate salt and interacts with other polar groups in the chondroitin sulfate chain, thereby causing bridging between UTI molecules. Several properties of UTI may be related to this interaction of Ca2+ with chondroitin sulfate chains. © 2001 Elsevier Science B.V.