A new method for converting commodity polymeric materials into value-added specialty materials was developed via site-selective and chemoselective transesterification of block copolymers, statistical copolymers, and homopolymers.

HIV-1 protease is an essential enzyme for viral particle maturation and is a target in the fight against HIV-1 infection worldwide. Several natural polymorphisms are also associated with drug resistance. Here, we utilized both pulsed electron double resonance, also called double electron-electron resonance, and NMR ¹⁵N relaxation measurements to characterize equilibrium conformational sampling and backbone dynamics of an HIV-1 protease construct containing four specific natural polymorphisms commonly found in subtypes A, F, and CRF_01 A/E. Results show enhanced backbone dynamics, particularly in the flap region, and the persistence of a novel conformational ensemble that we hypothesize is an alternative flap orientation of a curled open state or an asymmetric configuration when interacting with inhibitors.

Site-directed spin labeling with continuous wave electron paramagnetic resonance (EPR) spectroscopy was utilized to characterize dynamic features of the kink–turn motif formed through a leader–linker interaction in the Vibrio cholerae glycine riboswitch. Efficient incorporation of spin-labels into select sites within the phosphate backbone of the leader–linker region proceeded via splinted ligation of chemically synthesized spin-labeled oligonucleotides to in vitro transcribed larger RNA fragments. The resultant nitroxide EPR line shapes have spectral characteristics consistent with a kink–turn motif and reveal differential backbone dynamics that are modulated by the presence of magnesium, potassium, and glycine.

Electron paramagnetic resonance (EPR) spectroscopy coupled with site‐directed spin labeling (SDSL) is a valuable tool for characterizing the mobility and conformational changes of proteins but has seldom been applied to intrinsically disordered proteins (IDPs). Here, IA₃ is used as a model system demonstrating SDSL‐EPR characterization of conformational changes in small IDP systems. IA₃ has 68 amino acids, is unstructured in solution, and becomes α‐helical upon addition of the secondary structural stabilizer 2,2,2‐trifluoroethanol (TFE). Two single cysteine substitutions, one in the N‐terminus (S14C) and one in the C‐terminus (N58C), were generated and labeled with three different nitroxide spin labels. The resultant EPR line shapes of each of the labels were compared and each reported changes in mobility upon addition of TFE. Specifically, the spectral line shape parameters h₍₊₁₎/h₍₀₎, the local tumbling volume (V_L), and the percent change of the h₍₋₁₎ intensity were utilized to quantitatively monitor TFE‐induced conformational changes. The values of h_(+1)/h₍₀₎ as a function of TFE titration varied in a sigmoidal manner and were fit to a two‐state Boltzmann model that provided values for the midpoint of the transition, thus, reporting on the global conformational change of IA₃. The other parameters provide site‐specific information and show that S14C‐SL undergoes a conformational change resulting in more restricted motion than N58C‐SL, which is consistent with previously published results obtained by studies using NMR and circular dichroism spectroscopy indicating a higher degree of α‐helical propensity of the N‐terminal segment of IA₃. Overall, the results provide a framework for data analyzes that can be used to study induced unstructured‐to‐helical conformations in IDPs by SDSL.