TAFA5/FAM19A5: Proteins and Enzymes

TAFA5 (also FAM19A5) is a 14 kDa type I transmembrane protein and member of the FAM19/TAFA family of chemokine-like proteins. Human TAFA5 is 132 amino acids (aa) in length. It contains a 15 aa extracellular domain, a 23 aa transmembrane sequence, and a 95 aa cytoplasmic region. Alternate splicing produces two additional isoforms. Isoform 2, a secreted form, has a 31 aa substitution for residues 1-38 in isoform 1. Isoform 3 has an eight aa substitution for residues 1-87 in isoform 1. Human TAFA5 is 100% aa identical to mouse TAFA5. Within the TAFA family, TAFA5 is the most distinct member, while TAFAs 2, 3, and 4 are the most closely related members. Real-time PCR analysis indicates that TAFA5 mRNA expression is restricted to the central nervous system (CNS), with the highest level in the basal ganglia and cerebellum. The biological functions of TAFA family members are not yet known, but there are a few tentative hypotheses. First, TAFAs may modulate immune responses in the CNS by functioning as brain-specific chemokines, and may act with other chemokines to optimize the recruitment and activity of immune cells in the CNS. Second, TAFAs may represent a novel class of neurokines that act as regulators of immune nervous cells. Finally, TAFAs may control axonal sprouting following brain injury.