Glycosaminoglycan-mediated leuserpin-2/thrombin interaction. Structure-function relationships.

Two recently identified structural elements important for glycosaminoglycan-mediated activation of human leuserpin-2 (hLS2) were investigated in detail by functional analysis of variants secreted by transiently transfected COS cells. Highly specific requirements with respect to the nature of the involved amino acids as well as to their spatial arrangements were found to be crucial for efficient activation of hLS2 by dermatan sulfate. In contrast, binding and activation of hLS2 by heparin seem to be determined mainly by the positive charge density of the involved inhibitor segment. A dimeric repeat enriched in acidic amino acids turned out to exert a dual role with respect to structure and function of hLS2. First, in the absence of functional activators the negatively charged dimer interacts intramolecularly with the glycosaminoglycan-binding site. Second, the acidic dimer is instrumental in glycosaminoglycan-mediated activation of hLS2. The monomers constituting the acidic dimer are functionally not equivalent.