Proteins appear to transform more often than biologists once thought. Cutting and rearrangement of the components of these molecules into new structures is carried out by the human cells.
The immune system of the body may be enhanced by this mechanism. This method could also help researchers understand better how the immune system recognizes the infected cells that need to be attacked.
Depending on the specific type of protein required, an RNA template, produced by the DNA, is cut and rearranged. It has been assumed by biologists for a long period that rearrangement occurs only at the RNA level. However, in 2004, scientists found that this was not the case in proteins found in skin-cancer cells. These molecules, at protein level, seem to undergo rearrangement. This type of 'Protein Surgery' has been reported in plants and single-celled organisms.
Recently, it was reported by Edus Warren of the Fred Hutchinson Cancer Research Center in Seattle, Washington, and his colleagues that cutting and modification took place at protein level in some normal cells. They have reported in this week's Science that proteins can undergo chopping and alteration to produce a variety of structures from the original protein.
Peptides, a group of short proteins found on cell surface, were studied by the team. T-cells use these peptides to identify a foreign body. Degradation of proteins by cell machinery called the proteasome, which digests the proteins and cuts it into pieces, leads to the formation of peptides.
"The proteasome can splice peptides together," says Warren. "Every once in a while, new peptide bonds will be created, not just destroyed. It isn't clear why this happens, or what the newly spliced peptides do. But as the molecules end up on the cell's surface, they are probably involved in the cell's "immunologic identity"," he says.
According to a recent study, peptides, made in this manner found on cells from a leukaemia patient who had received a bone-marrow transplant, activated an immune response from the Tcells in the transplanted marrow.
Scientists contemplate that peptide splicing may enhance the immune system's recognition of virus infected cells. Since viruses replicate inside the cell, they could produce new peptides on the cell surface, whose subsequent rearrangement may improve the chances of the immune system to recognize the invader.
Whether all cells use their proteasomes to rearrange all types of proteins, or whether the mechanism is specific to peptides used by the immune system, is still unclear.
Warren believes that the mechanism will be found elsewhere. "There is no reason why cells could not have learned how to use this mechanism to their advantage. But I don't think that people have ever looked," he says.