Alignment of siglec-5, OB-BP1, human CD33, human MAG and the first two domains of mouse sialoadhesin. Sialoadhesin is included as a reference for amino acids that are important in sialic acid binding.10 Alignment was performed with the ClustalW multiple sequence alignment program, version 1.7 and optimized by eye. Residues that are identical in at least half the proteins are boxed in black, similar residues are in grey. Open boxes group the characteristic cysteine residues of siglec proteins and the residues that are important for interaction with sialic acid.10 The positions of the βstrands in domains 1 and 2 are indicated. The beginning of the transmembrane (TM) and cytoplasmic (CYTO) regions are indicated. Genbank accession numbers of OB-BP1, CD33, MAG, and sialoadhesin are U71382, M23197,M29273, and Z36293, respectively.