SIGLECs are cell surface proteins of the Ig superfamily. Most SIGLECs have 1 or more cytoplasmic immune receptor tyrosine-based inhibitory motifs, or ITIMs. A large subgroup of SIGLECs share high homology with SIGLEC3 (CD33) and are localized to 19q13.4. The cDNA for the SLG gene encodes 2 variants, SLG-long (SLGL) and SLG-short (SLGS). The 595-amino acid SLGL protein contains a signal peptide and 2 V-set N-terminal Ig-like domains. The 477-amino acid SLGS protein has a weak signal sequence and, like most SIGLEC3-like SIGLECs, has only 1 V-set N-terminal Ig-like domain. Both variants contain 2 C2-set N-terminal Ig-like domains, a transmembrane domain, and a cytoplasmic tail with a putative ITIM and a putative SLAM-like tyrosine-based motif. The conserved arginine residue thought to be essential for sialic acid binding in other SIGLECs is replaced by a glutamine in SLGS and by a cysteine in SLGL. RT-PCR analysis detected high expression of both variants in spleen and small intestine, and SLGS was highly expressed in adrenal gland and SLGL was highly expressed in bone marrow.

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