IDENTIFICATION OF A DOMAIN IN APOLIPOPROTEIN B-100 THAT INHIBITS THE PROCOAGULANT ACTIVITY OF TISSUE FACTOR

The ability of low-density lipoprotein (LDL) to inhibit the procoagula nt activity of tissue factor is mediated by a direct protein-protein i nteraction involving apolipoprotein (apo) B-100. A lysine-rich sequenc e within apo B-100 (residues 3121-3217), which we have termed lysine-r ich apo B-100-derived (KRAD)-98 peptide, may be responsible for its ac tivity. Within this region, residues 3147-3160 (KRAD-14) contain an ex ceptionally high proportion of positive amino acids. Both recombinant KRAD-98 and KRAD-14 peptides inhibited the procoagulant activity of ti ssue factor by preventing the activation of factor VII. KRAD-14 also i nhibited the prothrombinase components, factors Xa and V. In compariso n with the parent protein (apo B-100), KRAD-14 peptide displayed a 20- fold enhancement in the rate of inhibition, whereas KRAD-98 peptide ex hibited a rate closer to that of apo B-100. Mutational analysis of KRA D-14 peptide revealed three adjacent amino acids, alteration of which greatly reduced the inhibitory potential of this peptide. A peptide de rived from tissue factor (residues 58-66) was found to act co-operativ ely with tissue factor itself, but also augmented the inhibition of ti ssue-factor activity by apo B-100. In conclusion, LDL may be a physiol ogical regulator of haemostatic mechanisms through the interactions of lysine-rich domains of apo B-100 with tissue factor.