A NEW MUTATION DESTROYING DISULFIDE BRIDGING IN THE C-TERMINAL DOMAINOF LIPOPROTEIN-LIPASE

Lipoprotein lipase (LPL) is one of two intravascular lipases involved in the lipolysis of the triglyceride core of circulating lipoproteins. The occurrence of patients with genetic deficiencies has provided ins ight into the structure and function relationships of this lipase. it is now known that LPL manifests a two domain structure with the N-term inal domain of greater structural and functional significance as it co ntains the active sire and interfacial binding motifs. We report on a Cys418Tyr substitution in the C-terminal domain which disrupts the onl y disulphide bridge in the region and is associated with catalytic def iciency in postheparin plasma. This result was unexpected as previous in vitro assessment of the functional significance of disulphide bridg ing had shown that while the 3, N-terminal disulphides were critical f or enzyme function, loss of the only C-terminal disulphide minimally a ffected catalytic activity. We generated the Cys418Tyr mutant by site- directed mutagenesis and show that it manifests 48% of normal activity in vitro, while the companion variants, Cys438Ser and Cys418Ser-Cys43 8Ser, are less affected with activities at 76% and 78% of normal. (C) 1996 Academic Press, Inc.