The recent discovery that proteins can “edit” other proteins defies textbook beliefs about the known role of proteins. The study, published in the journal Science, suggests that certain proteins are capable of filling a role previously thought to be limited to messenger RNA (mRNA) and has molecular biologists blown away.
Proteins are made up of chains of amino acids, put together in a specific order as instructed by DNA encoding. Within the nucleus of a cell, the DNA instruction is copied to give the cell the necessary blueprints to create a specific protein. That copy is called RNA. The RNA is sent to the cytoplasm of the cell to be decoded, at which point the instructions are given to the messenger RNA (mRNA) and are sent to ribosomes where the protein is built. Transfer RNA (tRNA) uses that blueprint to construct the protein based on the exact order in which the amino acids should be linked.
The building of a protein does not always go as planned, however, and when something goes wrong during its creation, a cleanup crew is sent in, the ribosome is dismantled, the code is discarded and the attempted protein is recycled within the cell. That is the basic information you will find in biology textbooks today. According to the recent findings, there is another possible outcome for the flawed protein creation.
Part of the cleanup crew sent in to keep the faulty proteins from harming cell function is a protein called Rqc2. What the researchers uncovered about Rqc2 is that, before the incomplete protein can be recycled, Rqc2 will act in place of the mRNA and give an instruction to finish building the protein without the DNA code, but with a seemingly random order of just two of the 20 available amino acids. The protein’s creation continues with only threonine and alanine amino acids until the proper sequence can be resumed, reports UPI. During the time protein construction is stalled to allow for the cleanup crew to take care of the mistake, the Rqc2 protein prompts the ribosome to remain intact and gives the tRNA enough information to continue construction with the two amino acids.
There is little likelihood the randomly assorted protein is capable of proper function, leading scientists to believe that the true purpose of the Rqc2’s instructions may be to mark the protein for later destruction or to test the ribosome to determine whether it is functioning properly. If the Rqc2 is acting as protein quality control within the cell, the researchers say, studying it could provide great insights into what causes neurodegenerative diseases like Huntington’s and Alzheimer’s and could become a key in treatment. Faulty protein construction is thought to be at least part of the cause of such diseases, so understanding what makes the Rqc2 spring into action could help scientists develop a way to fix poor quality control mechanisms in the cell’s protein-building process. Proper protein function is required for a great many tasks from disease-fighting to the muscle contraction.
Using a technique called cryo-electron microscopy, the researchers flash-froze and visualized the cell’s quality control processes and found the Rqc2 handing out the instructions for the first time. Adam Frost, one of the study’s researchers, says the team felt the onus was on them to prove this shocking hypothesis. Thanks to extensive fine-tuning and biochemical analysis, they were able to observe the odd amino acid chain sequencing and link it to the previously unknown Rqc2 function.
By Sree Aatmaa Khalsa