As is typical for human proteins, over one third of the amino acids that make up NHERF1 were predicted to be intrinsically disordered, forming no known structures and matching no known evolutionarily-conserved pattern. According to Roder, it is one of these disordered segments, approximately 100 amino acids long, which enable the protein to work. That is, it allows the PDZ binding module to "bite" its own ezrin-binding tail, effectively shutting the protein down. "The flexibility of the linker and its tendency to be more or less disordered are critical for regulating the balance between internal ("autoinhibitory") forces and external interactions with the protein's signaling partners" Roder says. This idea is reinforced by a recent observation by Zimei Bu, Ph.D., a Fox Chase researcher a coauthor of this study, who found that enzymatic modification (phosphorylation) of amino acids in the disordered region tips the balance towards the more open, active, form of the protein.
"Evolution has provided researchers with convenient modular structures, areas that are repeated over and over again to make up proteins, and so we tend to dismiss the interspersed disordered sequences that don't seem to have any definable structure," Roder says. "Here we show that the weak molecular interactions in a disorganized protein sequence are essential in giving this protein its unique attributes."
It was also this disorganized domain that made it difficult for researchers to create an accurate model of the entire protein, Roder says. Typically, researchers use a technique called x-ray crystallography, in which they can tell a protein's structure from how crystals made from the protein samples scatter x-rays. The disorganized section of NHREF1 makes it nearly impossible to create the necessary crystals to use this technique. Instead, Roder and colleagues used a technique called nuclear magnetic
|Contact: Greg Lester|
Fox Chase Cancer Center