LAP

Alias: Pro-TGF beta 1, LAP/TGF beta 1, Latency Associated Peptide

TGFβ protein is synthesized as a precursor that contains LAP at the N-terminus and mature TGFβ at the C-terminus. The presence of LAP inhibits the biological activity of TGFβ to allow it to be secreted in a latent/inactive form. LAP must be dissociated from TGFβ or be conformationally altered in order for TGFβ to be active. Processing and cleavage of the precursor protein between amino acids 278 and 279 results in the formation of LAP dimers and TGFβ dimers that then non-covalently associate with each other to form the small latent TGFβ complex. LAP is secreted and can be found in the extracellular matrix. Many different cells produce TGFβ and it mediates effects on the proliferation, differentiation and function of many cell types. In addition, LAP can also be expressed on platelets and activated regulatory T cells. It is believed that this surface-expressed LAP is due to the binding of LAP to GARP (LRRC32), which is a transmembrane protein that is also found at high levels on platelets and activated regulatory T cells. Additionally, it is thought that the detection of LAP in serum is a surrogate for determining the amount of TGFβ without having to process the sample with acid.