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

Abstract
Low 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.

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