Backbone Dynamics of the First, Second, and Third Immunoglobulin Modules of the Neural Cell Adhesion Molecule (NCAM)

Fuzzy domains: new way of describing flexibility and interdependence of the protein domains

We proposed the innovative method of domain identification based on the concept of the fuzzy domains. In this method each residue of the protein can belong to several domains simultaneously with certain weights, which reflect to what extent this residue shares the motion pattern of the given domain. Our method allows describing the fuzzy boundaries between the domains and the gradual changes of the motion pattern from one domain to the other. It provides the reasonable compromise between the continuous change of the protein dynamics from one residue to the other and the discrete description of the structure in terms of small number of domains. We suggested quantitative criterion, which shows the overall degree of domain flexibility in the protein. The concept of the fuzzy domains provides an innovative way of visualization of domain flexibility, which makes the gradual transitions between the domains clearly visible and comparable to available experimental and structural data. In the future, the concept of the fuzzy domains can be used in the coarse-grained simulations of the domain dynamics in order to account for internal protein flexibility.

The change of protein intradomain mobility on ligand binding: is it a commonly observed phenomenon?

Analysis of changes in the dynamics of protein domains on ligand binding is important in several aspects: for the understanding of the hierarchical nature of protein folding and dynamics at equilibrium; for analysis of signal transduction mechanisms triggered by ligand binding, including allostery; for drug design; and for construction of biosensors reporting on the presence of target ligand in studied media. In this work we use the recently developed HCCP computational technique for the analysis of stabilities of dynamic domains in proteins, their intrinsic motions and of their changes on ligand binding. The work is based on comparative studies of 157 ligand binding proteins, for which several crystal structures (in ligand-free and ligand-bound forms) are available. We demonstrate that the domains of the proteins presented in the Protein DataBank are far more robust than it was thought before: in the majority of the studied proteins (152 out of 157), the ligand binding does not lead to significant change of domain stability. The exceptions from this rule are only four bacterial periplasmic transport proteins and calmodulin. Thus, as a rule, the pattern of correlated motions in dynamic domains, which determines their stability, is insensitive to ligand binding. This rule may be the general feature for a vast majority of proteins.

HIV-1 Tat Is a Natively Unfolded Protein

Tat (transactivator of transcription) is a small RNA-binding protein that plays a central role in the regulation of human immunodeficiency virus type 1 replication and in approaches to treating latently infected cells. Its interactions with a wide variety of both intracellular and extracellular molecules is well documented. A molecular understanding of the multitude of Tat activities requires a determination of its structure and interactions with cellular and viral partners. To increase the dispersion of NMR signals and permit dynamics analysis by multinuclear NMR spectroscopy, we have prepared uniformly 15N- and 15N/13C-labeled Tat-(1-72) protein. The cysteine-rich protein is unambiguously reduced at pH 4.1, and NMR chemical shifts and coupling constants suggest that it exists in a random coil conformation. Line broadening and multiple peaks in the Cys-rich and core regions suggest that transient folding occurs in two of the five sequence domains. NMR relaxation parameters were measured and analyzed by spectral density and Lipari-Szabo approaches, both confirming the lack of structure throughout the length of the molecule. The absence of a fixed conformation and the observation of fast dynamics are consistent with the ability of Tat protein to interact with a wide variety of proteins and nucleic acid and support the concept of a natively unfolded protein.