Small Molecule Binding to Alzheimer’s Risk Factor CD33 Promotes Aβ Phagocytosis
Luke A. Miles, Stefan J. Hermans, Gabriela A.N. Crespi, Jonathan H. Gooi, Larissa Doughty, Tracy L. Nero, Jasmina Markulić, Andreas Ebneth, Berthold Wroblowski, Daniel Oehlrich, Andrés A. Trabanco, Marie-Laure Rives, Ines Royaux, Nancy C. Hancock, Michael W. Parker
Polymorphism in the microglial receptor CD33 gene has been linked to late-onset Alzheimer’s disease (AD) and reduced expression of the CD33 sialic acid-binding domain confers protection. Thus, CD33 inhibition might be an effective therapy against disease progression. Lack of progress towards discovery of selective CD33 inhibitors has been hampered by the absence of an atomic resolution structure. We report here the crystal structures of CD33 alone and bound to a subtype-selective sialic acid mimetic called P22 and use them to identify key binding residues by site-directed mutagenesis and binding assays to reveal the molecular basis for its selectivity towards sialylated glycoproteins and glycolipids. We show that P22, when presented on microparticles, increases uptake of the toxic AD peptide, Aβ, into microglial cells. Thus, the sialic acid-binding site on CD33 is a promising pharmacophore for developing therapeutics that promote clearance of the Aβ peptide that is thought to cause AD.