Novel site in lipoprotein lipase (LPL415-438) essential for substrate interaction and dimer stability

LPL, like other lipases, has the ability to hydrolyze water-insoluble lipid substrates, but the mechanism is incompletely understood. We previously de monstrated a 22-amino acid loop in the amino-terminal domain of LPL to be e ssential for interaction with lipid substrates (Dugi, K. A., H. L. Dichek, G. D. Talley, H. B. Brewer, Jr., and S. Santamarina-Fojo. 1992. J. Biol. Ch em. 267: 25086-25091) and mediation of substrate specificity (Dugi, IL A., H. L. Dichek, and S. Santamarina-Fojo. 1995. J. Biol. Chem. 270: 25396-2540 1). The carboxy-terminal domain, LPLA15-438, contains two highly conserved hydrophobic stretches, and represents a candidate region for substrate inte ractions. Specific point mutations or deletion of the region between the hy drophobic stretches (LPL419-430) caused up to 90% selective loss of hydroly zing activity against water-insoluble triolein, but not against water-solub le tributyrin, implicating a crucial function for LPL419-430 in the interac tion with lipid substrates. In contrast, mutations introduced into the hydr ophobic regions led to concomitant changes in tributyrin and triolein activ ities. The presence of an additional positive charge at position 416 yielde d a gain of function mutant with Mold increased activity. This mutant was a bout three times more stable at 37 degreesC than wild-type LPL, suggesting an important role for the hydrophobic regions in LPL dimer stability.ie In summary, our data demonstrate that the carboxy-terminal region LPL415-438 p lays an important role in both the interaction of LPL with lipid substrates and the stability of the LPL homodimer.-Keiper, T., J. G. Schneider, and K . A. Dugi. Novel site in lipoprotein lipase (LPL415-438) essential for subs trate interaction and dimer stability. In summary, our data demonstrate tha t the carboxy-terminal region LPL415-438 plays an important role in both th e interaction of LPL with lipid substrates and the stability of the LPL hom odimer.