NATIVE AND MULTIMERIC VITRONECTIN EXHIBIT SIMILAR AFFINITY FOR HEPARIN - DIFFERENCES IN HEPARIN-BINDING PROPERTIES INDUCED UPON DENATURATION ARE DUE TO SELF-ASSOCIATION INTO A MULTIVALENT FORM

For many years, the concept that the heparin-binding sequence is seque stered within vitronectin and exposed upon denaturation of the protein has guided experimental design and interpretation of related structur e-function studies on the protein, To evaluate binding of heparin to b oth native and denatured/renatured vitronectin, methods for monitoring binding in solution have been developed. A fluorescence method based on changes in an extrinsic probe attached to heparin has been used to evaluate heparin binding to native and denatured/renatured vitronectin . This approach indicates that there are not major differences in intr insic heparin-binding affinities between native and renatured protein and invalidate the currently accepted model for a cryptic heparin-bind ing sequence in the protein, Denaturation and renaturation oligomer, O n the basis of the binding data from solution studies and interaction of the native monomer and the denatured multimeric form of vitronectin with a heparin column, along with evaluation of the ionic strength de pendence of heparin binding to these vitronectin forms in solution, an alternative model is favored to account for the altered heparin bindi ng properties of vitronectin associated with denaturation of the prote in. This model proposes that multivalent interactions between heparin and multimeric vitronectin are responsible for differences in heparin affinity chromatography and ionic strength dependence compared with th e native protein.