Transmembrane 4 L Six Family, Member 18 (TM4SF18)

TM4SF18 also known as AAB5 and L6D, was cloned from human umbilical vein endothelial cells. It shares approximately 40 - 50% amino acid sequence identity with L6, IL-TMP, and TM4SF5, a group of proteins with limited homology to the tetraspanin superfamily.
TM4SF18 belongs to the L6 tetraspanin family, L6, IL-TMP, and TM4SF5 are cell surface proteins predicted to have four transmembrane domains. Previous sequence analysis led to their assignment as members of the tetraspanin superfamily.A new sequence (L6D) that is strikingly similar to L6, IL-TMP, and TM4SF5. Analyses of these four sequences indicate that they are not significantly related to genuine tetraspanins, but instead constitute their own L6 superfamily.