High affinity binding between lipoprotein lipase and lipoproteins involvesmultiple ionic and hydrophobic interactions, does not require enzyme activity, and is modulated by glycosaminoglycans

Lipoprotein lipase (LPL) physically associates with lipoproteins and hydrol yzes triglycerides. To characterize the binding of LPL to lipoproteins, we studied the binding of low density lipoproteins (LDL), apolipoprotein (apo) B17, and various apoB-FLAG (DYKDDDDK octapeptide) chimeras to purified LPL . LDL bound to LPL with high affinity (K-d values of 10(-12) M) similar to that observed for the binding of LDL to its receptors and 1D1, a monoclonal antibody to LDL, and was greater than its affinity for microsomal triglyce ride transfer protein. LDL-LPL binding was sensitive to both salt and deter gents, indicating the involvement of both hydrophobic and hydrophilic inter actions. In contrast, the N-terminal 17% of apoB interacted with LPL mainly via ionic interactions. Binding of various apoB fusion peptides suggested that LPL bound to apoB at multiple sites within apoB17, Tetrahydrolipstatin , a potent enzyme activity inhibitor, had no effect on apoB-LPL binding, in dicating that the enzyme activity was not required for apoB binding. LDL-LP L binding was inhibited by monoclonal antibodies that recognize amino acids 380-410 in the C-terminal region of LPL, a region also shown to interact w ith heparin and LDL receptor-related protein. The LDL-LPL binding was also inhibited by glycosaminoglycans (GAGs); heparin inhibited the interactions by similar to 50% and removal of trace amounts of heparin from LPL preparat ions increased LDL binding. Thus, we conclude that the high affinity bindin g between LPL and lipoproteins involves multiple ionic and hydrophobic inte ractions, does not require enzyme activity and is modulated by GAGs. It is proposed that LPL contains a surface exposed positively charged amino acid cluster that may be important for various physiological interactions of LPL with different biologically important molecules. Moreover, we postulate th at by binding to this cluster, GAGs modulate the association between LDL an d LPL and the in vivo metabolism of LPL.