Preliminary characterization of the protein encoded by human Testis-Enhanced Gene Transcript (TEGT)

Abstract

TEGT is a conserved, widely expressed gene transcript of unknown function that has been studied previously only at the nucleic acid level. The deduced amino acid sequence predicts a highly hydrophobic, 26.5 kDa integral membrane protein with seven potential transmembrane domains. Little else is known about TEGT protein because of the lack of definitive homology to other known sequences and the absence of informative consensus motifs. The present report details a preliminary study of human TEGT (hTEGT) protein, (i) In vitro translation of hTEGT in reticulocyte lysates required the presence of microsomes for efficient synthesis, suggesting that hTEGT must target to the endoplasmic reticulum to be translated. Immunofluorescence of cells transiently expressing haemagglutinin-tagged hTEGT localized the protein mainly to the endoplasmic reticulum. The protein demonstrated no obvious post-translational modifications such as signal-peptide cleavage, N-iinked glycosylation or O-linked glycosylation. (ii) Both hTEGT and haemagglutinin-tagged hTEGT appeared to retain partial secondary and tertiary structure in the presence of SDS. Both electrophoresed as a broad band or doublet with apparent molecular weights of 22–24.5 kDa on SDS-PAGE, aggregated either homotypically or heterotypically when boiled in SDS, and were toxic after 24 h when highly overexpressed in 293 T cells. These properties are believed to be caused by the protein's hydrophobicity. (iii) The protein appeared to associate strongly with other intracellular molecules since haemagglutinin-tagged hTEGT was extracted poorly from transiently transfected HeLa cells. Further study will be required to determine the cellular function of TEGT.

Key Words:

• integral membrane protein
• in vitro translation
• epitope-tagging
• immunofluorescence
• endoplasmic reticulum