Abstract
Intrinsically disordered proteins (IDPs) represent approximately 30% of the human genome and play key roles in cell proliferation and cellular signaling by modulating the function of target proteins via protein–protein interactions. In addition, IDPs are involved in various human disorders, such as cancer, neurodegenerative diseases, and amyloidosis. To understand the underlying molecular mechanism of IDPs, it is important to study their structural features during their interactions with target proteins. However, conventional biochemical and biophysical methods for analyzing proteins, such as X-ray crystallography, have difficulty in characterizing the features of IDPs because they lack an ordered three-dimensional structure. Here, we present biochemical and biophysical studies on nucleolar phosphoprotein 140 (Nopp140), which mostly consists of disordered regions, during its interaction with casein kinase 2 (CK2), which plays a central role in cell growth. Surface plasmon resonance and electron paramagnetic resonance studies were performed to characterize the interaction between Nopp140 and CK2. A single-molecule fluorescence resonance energy transfer study revealed conformational change in Nopp140 during its interaction with CK2. These studies on Nopp140 can provide a good model system for understanding the molecular function of IDPs.
Highlights
A well-defined tertiary structure was considered until recently to be the determining factor for biological and biochemical function of proteins
intrinsically disordered proteins (IDPs) harboring a defined disordered region or IDPs mostly comprising disordered regions are commonly observed in most organisms, and their significance in various biological phenomena is commonly observed in most organisms, and their significance in various biological phenomena is clear
These IDPs possess several motifs which can serve interest with respect to their mechanism of action. These IDPs possess several motifs which can serve as interaction sites for different binding proteins, and the activity of a binding protein can be modified as interaction sites for different binding proteins, and the activity of a binding protein can be modified upon interaction with IDPs
Summary
A well-defined tertiary structure was considered until recently to be the determining factor for biological and biochemical function of proteins. Active sites of enzymes or interaction domains of signaling proteins usually consist of amino acid residues in their tertiary structure. Stretches of amino acids lacking a stable tertiary structure are often found in linker regions between well-folded domains. The length of IDRs in these proteins is often characterized as having a high percentage of disorder-promoting residues [4] (Table 1). IDPs lack a well-folded domain structure, they have several motifs that can serve as interaction sites residues [4] (Table 1). These IDPs lack a well-folded domain structure, they have several with other biomolecules, such as DNA, RNA, or protein [5].
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