Targeting to the endoplasmic reticulum improves the folding of recombinant human telomerase reverse transcriptase

Telomerase is a specialized reverse transcriptase that catalyzes the addition of telomeric repeats, TTAGGG in all vertebrates, to the ends of chromosomes. The lack of recombinant purified human telomerase reverse transcriptase (hTERT) has hampered biochemical and structural studies. The primary problem in generating active recombinant hTERT appears to be protein folding, which may be due to the fact that telomerase is a multi-component ribonucleoprotein complex. When expressed in most heterologous systems, recombinant hTERT is largely insoluble. Here we describe a protein expression system using a baculovirus vector that can be used to prepare properly folded, enzymatically active, hTERT. In this system, the recombinant hTERT is directed to the endoplasmic reticulum (ER), which is rich in chaperones. This increases the expression of soluble recombinant hTERT, promoting proper folding using intrinsic ER chaperone proteins.