Siglec-E is a member of Siglec family of glycan recognition proteins involved in the regulation of myeloid cell activities. Siglec-E preferentially recognizes disialic acid, a glycan epitope consisting of two sialic acids conjugated in alpha2-8 linkage (Zhang JQ et al., Eur J Immunol. 2004, 34:1175-84). BCL-1, a mouse B cell line, expresses disialic acid epitope (Wang SH et al., Glycobiology. 2013, 23:677-89). In this experiment, we attempted at identifying the ligands of Siglec-E on BCL-1 by applying the proximity labeling method we developed (Chang L et al., J Proteome Res. 2017, 16:3929-41).