The T cell receptor-associated protein is proteolytically cleaved in a pre-Golgi compartment.
The TCR consists of at least seven transmembrane chains: the clonotypic disulfide-linked alpha- and beta-chains, the invariant gamma-, delta-, and epsilon-chains, termed the CD3 complex, and the zeta-zeta homodimer. We have recently described an additional 26-kDa protein, which is transiently associated with newly synthesized mouse CD3 chains in the endoplasmic reticulum. The exact function of this protein, which we called TRAP (for TCR-associated protein) is not yet known; studies suggest however, that it may play a role in the assembly of the TCR complex. Here we report the properties of another protein which has a Mr of 16,000 and, like TRAP, can be coimmunoprecipitated from metabolically labelled murine T cells with antibodies against the chains of the CD3 complex. Kinetic analysis suggests a precursor-product relationship between TRAP and the 16-kDa protein: the latter starts appearing once TRAP begin to disappear. Having reached a maximal level at approximately 1 h after biosynthesis, it is rapidly lost. Agents that slow or block the disappearance of TRAP, delay or prevent the appearance and eventual disappearance of the 16-kDa protein. Incubation of immunoprecipitates containing gamma, epsilon, and TRAP in vitro at 37 degrees C results in the appearance of the 16-kDa protein. Employing HPLC peptide mapping we demonstrate that this 16-kDa protein is structurally related to TRAP. These results suggest that the removal of TRAP from the newly synthesized CD3 chains is accompanied by its proteolytic cleavage in a pre-Golgi compartment.
Antusch
D
D
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institute of Health, Bethesda, MD 20892.
Bonifacino
J S
JS
Burgess
W H
WH
Klausner
R D
RD
D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D017252:CD3 Complex; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D051379:Mice; D010447:Peptide Hydrolases / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*
D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D011948:Receptors, Antigen, T-Cell; D010447:Peptide Hydrolases