Structural investigation of tumor differentiation factor

Tumor differentiation factor ( TDF ) is a 17 kDa protein produced by the pituitary and secreted into the bloodstream, with no definitive function and incomplete characterization. TDF has the following four cysteine ( C ys) residues: C ys17, C ys70, C ys97, and C ys98. To understand the function of TDF , we (1) overexpressed and characterized recombinant TDF (r TDF ); (2) investigated native, secreted TDF ; and (3) assessed potential disulfide connectivities using molecular modeling. Our results from W estern blotting ( WB ) experiments suggest that r TDF is mostly expressed as insoluble, monomeric, and dimeric forms. Mass spectrometry analysis of the overexpressed r TDF identified a peptide that is a part of TDF protein. WB of the native, secreted TDF detected it as a 50 kDa band. In addition, investigation of TDF by molecular modeling suggests that the C ys residues may form disulfide bridges between C ys17– C ys98 and C ys70– C ys17.