Decision letter: Single-molecule imaging of telomerase reverse transcriptase in human telomerase holoenzyme and minimal RNP complexes

Abstract

Enzymes carry out the many diverse chemical reactions that support life. Some enzymes are made of just one component protein that works on its own, but others are made of multiple proteins that are all required for the enzyme to work properly. Most of what is understood about the activities of enzymes has been deduced by studying solutions containing many enzyme molecules. However, many enzymes can bind to different combinations of proteins to form groups (or ‘complexes’) with a variety of three-dimensional shapes, so there may be a variety of enzyme complexes in the solution. This can lead to researchers drawing different conclusions about the same enzyme. In humans and other eukaryotic organisms, DNA is contained within structures called chromosomes. An enzyme called telomerase adds structures called telomeres to the ends of the chromosomes, which protect the DNA from damage. The center of telomerase has a protein called TERT that forms complexes with other proteins. However, it is not known how many copies of the TERT protein are present in each complex. Wu et al. studied these complexes using fluorescent tags that enabled each protein to be identified using a technique called ‘single-particle imaging’. The experiments show that these complexes can contain either one or two TERT proteins. It had previously been suggested that TERT is only an active enzyme when it is bound to another TERT molecule, but Wu et al. show that even complexes with a single TERT are able to add telomeres to DNA. Further experiments used a mutant form of the TERT protein that cannot interact with other TERT molecules and found that complexes that contain this mutant protein still have normal enzyme activity. Large quantities of purified proteins were used in this study. Therefore, a future challenge will be to refine the method to allow experiments to use much less protein, which would more closely reflect how telomerase is produced in cells.