Chymotryptic cleavage of lipoprotein lipase

Publisher Website
Google Scholar
Abstract
Treatment of bovine lipoprotein lipase (LPL) with chymotrypsin results in cleavage between residues Phe390‐Ser391 and between Trp392‐Ser393, indicating that this region is exposed in the native conformation of LPL. Two main fragments are generated, one large including the aminoterminus (chymotrypsin‐truncated LPL = c‐LPL) and one small, carboxy‐terminal fragment. The small fragment is not stable, but is further degraded by the protease. Isolated c‐LPL has full catalytic activity against tributyryl glycerol (tributyrin) and p‐nitrophenyl butyrate, while the activity against emulsions of long‐chain triacylglycerols and against liposomes is reduced and the activity against milk fat globules and chylomicrons is lost. Several properties of c‐LPL were investigated. It was found that c‐LPL interacts with apolipoprotein CII (apo CII) as efficiently as intact LPL. The truncated enzyme bound to liposomes and to emulsions of long‐chain triacylglycerols as well as the intact enzyme did. In contrast, c‐LPL did not bind to milk fat globules or to chylomicrons. The activity of c‐LPL was more sensitive to inhibition by other lipid‐binding proteins, e.g. apolipoprotein CIII (apo CIII), than was the intact enzyme. The affinity for heparin was as high with c‐LPL as with intact LPL. Like intact LPL, c‐LPL is dimeric in its active form, as evidenced by sucrose density gradient centrifugation.It is concluded that the reduced catalytic and lipid‐binding properties of c‐LPL compared with intact LPL are related to the properties of the substrate interface. It is speculated that the carboxyterminal part of LPL contains a secondary lipid‐binding site, which is important for activity against chylomicrons and related substrates.

This publication has 45 references indexed in Scilit: