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

Urinary trypsin inhibitor (UTI) has several roles other than protease inhib ition. It is suggested that UTI inhibits calcium influx in cultured cells a nd that the chondroitin sulfate chain of UTI may play an important role. In order to clarify the mechanistic features of this phenomenon, the chondroi tin sulfate chain of UTI was analyzed by H-1-NMR. The samples were highly p urified UTI dissolved in D2O in the presence or absence of Ca2+, Mg2+ and N a+. 1D-spectra were obtained and T-1 values of detected signals were estima ted from the inversion-recovery method. The addition of Ca2+ to UTI caused a chemical shift to downfield, line broadening and a reduction of T-1 value s at several signals from chondroitin sulfate moiety (especially at axial H -2 of GalNAc), whereas Mg2+ and Naf had no significant effect. Some of the signals in the linkage region of chondroitin sulfate chain showed marked li ne broadening by Ca2+. The reduction of T1 values implies formation of a co mplex. It is suggested that Ca2+ generates the sulfate salt and interacts w ith other polar groups in the chondroitin sulfate chain, thereby causing br idging between UTI molecules. Several properties of UTI may be related to t his interaction of Ca2+ with chondroitin sulfate chains. (C) 2001 Elsevier Science B.V. All rights reserved.