Although intrinsically disordered proteins (IDPs) are widespread in nature and play diverse and important roles in biology, they have to date been little characterized structurally. Auspiciously, intensified efforts using NMR spectroscopy have started to uncover the breadth of their conformational landscape. In particular, polypeptide backbone chemical shifts are emerging as powerful descriptors of local dynamic deviations from the "random coil" state toward canonical types of secondary structure. These digressions, in turn, can be connected to functional or dysfunctional protein states, for example, in adaptive molecular recognition and protein aggregation. Here we describe a first inventory of IDP backbone (15)N, (1)H(N), (1)H(α), (13)C(O), (13)C(β), and (13)C(α) chemical shifts using data obtained for a set of 14 proteins of unrelated sequence and function. Singular value decomposition was used to parametrize this database of 6903 measured shifts collectively in terms of 20 amino acid-specific random coil chemical shifts and 40 sequence-dependent left- and right-neighbor correction factors, affording the ncIDP library. For natively unfolded proteins, random coil backbone chemical shifts computed from the primary sequence displayed root-mean-square deviations of 0.65, 0.14, 0.12, 0.50, 0.36, and 0.41 ppm from the experimentally measured values for the (15)N, (1)H(N), (1)H(α), (13)C(O), (13)C(β), and (13)C(α) chemical shifts, respectively. The ncIDP prediction accuracy is significantly higher than that obtained with libraries for small peptides or "coil" regions of folded proteins.

ATP-binding cassette (ABC) transporters use the energy of ATP hydrolysis to move molecules through cellular membranes. They are directly linked to human diseases, cancer multidrug resistance, and bacterial virulence. Very little is known of the conformational dynamics of ABC transporters, especially at the single-molecule level. Here, we combine single-molecule spectroscopy and a novel molecular simulation approach to investigate the conformational dynamics of the ABC transporter BtuCD. We observe a single dominant population of molecules in each step of the transport cycle and tight coupling between conformational transitions and ligand binding. We uncover transient conformational changes that allow substrate to enter the transporter. This is followed by a 'squeezing' motion propagating from the extracellular to the intracellular side of the translocation cavity. This coordinated sequence of events provides a mechanism for the unidirectional transport of vitamin B by BtuCD.

Highlights d A method is developed to study allosteric communications in ABC transporters d The outcome of engineered mutations is computationally predicted d Experiments show that the predictions are highly accurate d Different allosteric pathways give rise to different transport mechanisms

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Oligomerization of Pr55Gag is a critical step of the late stage of the HIV life cycle. It has been known that the binding of IP6, an abundant endogenous cyclitol molecule at the MA domain, has been linked to the oligomerization of Pr55Gag. However, the exact binding site of IP6 on MA remains unknown and the structural details of this interaction are missing. Here, we present three high-resolution crystal structures of the MA domain in complex with IP6 molecules to reveal its binding mode. Additionally, extensive Differential Scanning Fluorimetry analysis combined with cryo- and ambient-temperature X-ray crystallography and GNM-based transfer entropy calculations identify the key residues that participate in IP6 binding. Our data provide novel insights about the multilayered HIV-1 virion assembly process that involves the interplay of IP6 with PIP2, a phosphoinositide essential for the binding of Pr55Gag to membrane. IP6 and PIP2 have neighboring alternate binding sites within the same highly basic region (residues 18–33). This indicates that IP6 and PIP2 bindings are not mutually exclusive and may play a key role in coordinating virion particles’ membrane localization. Based on our three different IP6-MA complex crystal structures, we propose a new model that involves IP6 coordination of the oligomerization of outer MA and inner CA domain’s 2D layers during assembly and budding.