Recombinant lecithin:cholesterol acyltransferase containing a Thr123-->Ile mutation esterifies cholesterol in low density lipoprotein but not in high density lipoprotein.

Fish-eye disease is a rare genetic disorder of high density lipoprotein (HDL) metabolism that is characterized bi- ochemically by a partial deficiency of the enzyme leci- thin:cholesterol acyltransferase (LCAT). One of the mutations that is causative for fish-eye disease occurs at codon 123 of the LCAT gene. This mutation results in the exchange of a threo- nine residue for an isoleucine in the LCAT protein (Thr123+Ile). In order to understand the functional significance of this exchange, we have used site-directed mutagenesis to reconstruct this mutation in an LCAT cDNA followed by expres- sion of the mutant LCAT in COS-1 cells. The fish-eye disease mutation resulted in a 50% decrease in LCAT mass in the cul- ture medium compared to wild type enzyme. The secreted mu- tant protein was incapable of esterifying cholesterol in HDL and HDL analogues. However, this protein retained the ability to es- terify cholesterol in plasma and low density lipoprotein. These results support the hypothesis that this mutation is responsible for biochemical abnormalities of LCAT observed in fish-eye dis- ease and the mutant LCAT protein has lost the potential to es- terify cholesterol in the HDL pool but retains the ability to es- terify cholesterol from other lipoproteins.-0, K., J. S. Hill, X. Wang, and P. H. Pritchard. Recombinant 1ecithin:cholesterol acyltransferase containing a Thr,z3+Ile mutation esterifies cholesterol in low density lipoprotein but not in high density lipoprotein. J: Lipid Res. 1993. 34: 81-88.