Submitted June 8, 2007
Accepted July 12, 2007
The Laminin 511/521 binding site on the Lutheran blood group glycoprotein is located at the flexible junction of Ig domains 2 and 3
Tosti J Mankelow*, Nicholas Burton, Fanney O Stefansdottir, Frances A Spring, Stephen F Parsons, Jan S Pedersen, Cristiano LP Oliveira, Donna Lammie, Timothy Wess, Narla Mohandas, Joel Anne Chasis, R Leo Brady, and David J. Anstee
Cell Adhesion, Bristol Institute for Transfusion Sciences, National Blood Service, Bristol, United Kingdom
Department of Biochemistry, University of Bristol, Bristol, United Kingdom
Department of Chemistry, University of Aarhus, Aarhus, Denmark
School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
Red Cell Physiology, New York Blood Center, New York, NY, United States
Life Sciences Division, University of California, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
* Corresponding author; email: tosti.mankelow{at}nbs.nhs.uk.
The Lutheran blood group glycoprotein, first discovered on erythrocytes, is widely expressed in human tissues. It is a ligand for the 
5 subunit of Laminin 511/521, an extracellular matrix protein. This interaction may contribute to vasocclusive events that are an important cause of morbidity in sickle cell disease. Using X-ray crystallography, small angle X-ray scattering and site directed mutagenesis we show that the extracellular region of Lutheran forms an extended structure with a distinctive bend between the second and third immunoglobulin-like domains. The linker between domains 2 and 3 appears to be flexible and is a critical determinant in maintaining an overall conformation for Lutheran that is capable of binding to Laminin. Mutagenesis studies indicate that Asp312 of Lutheran and the surrounding cluster of negatively charged residues in this linker region form the Laminin binding site. Unusually, receptor binding is therefore not a function of the domains expected to be furthermost from the plasma membrane. These studies imply that structural flexibility of Lutheran may be essential for its interaction with Laminin and present a novel opportunity for the development of therapeutics for sickle cell disease.
