Proposed lipocalin fold for apolipoprotein M based on bioinformatics and site-directed mutagenesis

Apolipoprotein RI (apoM) is a novel apolipoprotein that is predominantly pr esent in high-density lipoprotein, Sensitive sequence starches, threading a nd comparative model building experiments revealed apoM to be structurally related to the lipocalin protein family. In a 3D model, characterized by an eight-stranded anti-parallel beta -barrel, a segment including Asn135 coul d adopt a closed or open conformation. Using site-directed mutagenesis, we demonstrated Asn135 in wild-type apoM to be glycosylated, suggesting that t he segment is solvent exposed, ApoM displays two strong acidic patches of p otential functional importance, one around the N-terminus and the other nex t to the opening of the beta -barrel. (C) 2001 Federation of European Bioch emical Societies. Published by Elsevier Science B,V. All rights reserved.