ANIONIC PHOSPHOLIPIDS BIND TO L-SELECTIN (BUT NOT E-SELECTIN) AT A SITE DISTINCT FROM THE CARBOHYDRATE-BINDING SITE

It is known that L-selectin binds to glycoconjugates containing the te trasaccharide sialyl Lewis X in a Ca2+-dependent manner. In addition, a number of other acidic oligosaccharides (for example heparin or chon droitin sulphate) or glycolipids (for example sulphatides) bind to L-s electin independent of cations. In this paper we have established that L-selectin binds to charged phospholipids, such as cardiolipin and ph osphatidylserine, but not to neutral phospholipids such as phosphatidy lcholine. No interaction between E-selectin and any phospholipid was o bserved. The interaction between L-selectin and cardiolipin was inhibi ted by dextran sulphate, fucoidan, mannose 6-phosphate and monoclonal antibodies previously reported to block the interaction between L-sele ctin and its natural ligands. Analysis of the amino acid sequence of t he selectins indicated that L-selectin, but not E-selectin, contains a sequence homologous to the putative cardiolipin-binding epitope found in plasma glycoprotein beta(2)I. Glycoprotein beta(2)I and a peptide corresponding to the putative cardiolipin-binding epitope in beta(2)I inhibited the binding of L-selectin to cardiolipin or fucoidin. Based on the binding characteristics, sequence analysis and structural model ling of L-selectin, we suggest that the amino acid sequence KKNKED (re sidues 84-89) is a novel site for the binding of acidic species to L-s electin, This motif is localized close to the putative carbohydrate-bi nding domain of L-selectin and may be a second site within the lectin domain for the interaction of leucocyte L-selectin with its natural en dothelial ligands.