The tumor necrosis factor (TNF) superfamily is a protein superfamily of type II transmembrane proteins containing TNF homology domain and forming trimers. Members of this superfamily can be released from the cell membrane by extracellular proteolytic cleavage and function as a cytokine.

1. TNF Superfamily
The tumor necrosis factor (TNF) superfamily is a protein superfamily of type II
transmembrane proteins containing TNF homology domain and forming trimers.
Members of this superfamily can be released from the cell membrane by
extracellular proteolytic cleavage and function as a cytokine. These proteins are
expressed predominantly by immune cells and regulate diverse cell functions,
including regulation of immune response and inflammation, and proliferation,
differentiation, apoptosis and embryogenesis. The superfamily contains 19 members
that bind to 29 members of TNF receptor superfamily. An occurrence of orthologs in
invertebrates hints at ancient origin of this superfamily in evolution.
The PROSITE pattern of this superfamily is located in a beta sheet in the central
section of the protein that is conserved across all members.
Lymphotoxin-alpha (LT-α) or tumor necrosis factor-beta (TNF-β) is a protein that in
humans is encoded by the LTA gene. Belonging to the hematopoietic cell line, LT-α
exhibits anti-proliferative activity and causes the cellular destruction of tumor cell
lines. As a cytotoxic protein, LT-α performs a variety of important roles in immune
regulation depending on the form that it is secreted as. In other words, LT-α has both
a membrane-bound and soluble form that perform distinct roles in immune
regulation. The human gene encoding for LT-α was cloned in 1985. The gene of LT-α
is located on chromosome 6 and is in close proximity of the gene encoding major
histocompatibility complex. LT-α is translated as a 25 kDa glycosylated polypeptide
with 171 amino acid residues. Furthermore, human LT-α is 72% identical to mouse
LT-α at the protein's primary sequence.
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