Biochemical analysis of a T cell receptor alpha-like molecule involved in antigen-nonspecific suppression

Monoclonal nonspecific suppressor factor (MNSF), a lymphokine produced by murine T cell hybridoma, possesses a pleiotropic antigen-nonspecific suppressive function. We have shown that 70 kDa MNSF comprises an 8 kDa ubiquitin-like polypeptide (Ubi-L) and 62 kDa T cell receptor (TCR) alpha-like molecule. Ubi-L binds specifically to its 82 kDa receptor protein on target cells. In the current study, we have further characterized the biochemical nature of the TCR(alpha)-like molecule. The 62 kDa protein was separated into two species of 46 kDa and 16 kDa on reverse-phase HPLC. Anti-TCR(alpha) monoclonal antibody recognized the 46 kDa, but not the 16 kDa protein. Anti-TCRbeta monoclonal antibody failed to recognize these proteins. Ubi-L conjugated to the 46 kDa protein, whereas Ubi-L lacking its C-terminal Gly-Gly did not. Although Ubi-L was labile both to heating at 56 degrees C and to acidification to pH 4, the Ubi-L-46 kDa protein complex was unaffected by these treatments. In addition, the 46 kDa protein elongated the Ubi-L-induced protein tyrosine phosphorylation in a concanavalin A-activated murine T helper type 2 clone, D10 cells. One of the four tryptic peptide sequences derived from the 46 kDa protein was in alignment with a related sequence found in the J(alpha) region of the TCR(alpha), including the highly conserved motif F-G-X-G-T-X-L.