Utrecht University: No signal function for histidine in mammalian cells

Phosphorylation is the process in living cells in which a phosphate group is attached to one of the building blocks of a protein. “These modifications of proteins function like an on-off switch, so to speak, and ensure the transmission of signals between proteins,” says Simone Lemeer of Utrecht University’s Bijvoet Centre for Biomolecular Research. “In animals, it was already known that this is possible for three of these protein building blocks: the amino acids tyrosine, threonine and serine. In bacteria, it also occurs via four other amino acids, including histidine.”

For years, the conclusions of the American scientists were adopted, without being able to verify their results. We can now prove that it is not true.

Simone Lemeer
Metabolic instead of signalling function
The scientific journals Nature, PNAS and Cell, among others, have published articles claiming that the phosphorylation of histidine for signal transmission also exists in mammalian cells. Lemeer: “Some reputable American researchers say that histidine phosphorylation in mice causes cancer and metastases. That implies communication between cells and therefore signal exchange between proteins in those cells.”

Biomolecular scientist Lemeer and former PhD student Niels Leijten had very different results: “We indeed found histidine phosphorylation for transmitting signals in bacteria, but not in human cells.”

In five cases, the Utrecht researchers did find phosphorylation of histidine in human cells, but these did not have a signalling function. “They were used as intermediates,” Lemeer explains. “They only pass on phosphate to another molecule. That has a so-called metabolic function, for example to make energy-carrying molecules or building blocks for DNA and RNA. These processes exist to keep the cell going. The signalling function, on the other hand, is able to initiate a change in the cell, such as the expression of other genes, leading, for example, to division or growth of the cell.”

True until proven otherwise
The American authors had based their results on research using antibodies. “But that doesn’t allow you to look at specific locations in a protein,” says Lemeer. “Phosphorylated histidine is very labile anyway: the phosphate group falls off immediately and is therefore difficult to detect, whereas in the other three amino acids it is much more stable. At the UU we have developed a new method based on advanced mass spectrometry, with which we can specifically see to which amino acid in the protein the phosphate group binds.”

Lemeer is looking forward to the scientific discussion in her field. “For years, the conclusions of the American scientists were adopted, without being able to verify their results. By systematically scrutinizing our data, we can now prove that it is not true. The evidence is simply not there. This publication shows the power of science: something is true until proven otherwise.”