β-Sheet secondary structure of an LDL receptor domain from complement factor I by consensus structure predictions and spectroscopy

AbstractLow density lipoprotein receptor domains (LDLrs) represent a large cell surface receptor superfamily of consensus length 39 residues. Alignment of 194 sequences indicated highly conserved Cys and Asp/Glu residues, and a consensus secondary structure with three β-strands was predicted. Sequence threading against known protein folds indicated consistency with small β-sheet proteins. Complement factor I contains two LDLrs, and the second of these was successfully expressed using a bacterial pGEX system. FT-IR spectroscopy on this indicated a small amount of β-sheet together with turns and loops. LDLr is proposed to have a β-sheet structure in which the five biologically important Asp/Glu residues are located on an exposed loop