Ultrafast dynamics of water in cationic micelles

The effect of confinement on the dynamical properties of liquid water is investigated for water enclosed in cationic reverse micelles. The authors performed mid-infrared ultrafast pump-probe spectroscopy on the OH-stretch vibration of isotopically diluted HDO in D(2)O in cetyltrimethylammonium bromide (CTAB) reverse micelles of various sizes. The authors observe that the surfactant counterions are inhomogeneously distributed throughout the reverse micelle, and that regions of extreme salinity occur near the interfacial Stern layer. The authors find that the water molecules in the core of the micelles show similar orientational dynamics as bulk water, and that water molecules in the counterion-rich interfacial region are much less mobile. An explicit comparison is made with the dynamics of water confined in anionic sodium bis(2-ethythexyl) sulfosuccinate (AOT) reverse micelles. The authors find that interfacial water in cationic CTAB reverse micelles has a higher orientational mobility than water in anionic AOT reverse micelles.     

Energy relaxation dynamics of the hydration complex of hydroxide

We use polarization-resolved mid-infrared pump-probe spectroscopy to study the dynamics of the hydration shells of hydroxide ions (OH(-)). We excite the OH stretch vibrations of H(2)O molecules solvating the OH(-) ion and observe that this excitation decays with a relaxation time constant T(1) of 200 fs. This relaxation is followed by a thermalization process that becomes slower with increasing concentration of OH(-). The prethermalized state is observed to be anisotropic, showing that the energy of the excited OH stretch vibrations is dissipated within the hydration complex. The anisotropy of the prethermalized state decays both as a result of the reorientation of the OH(-) hydration complex and heat diffusion from the excited complexes to unexcited complexes. Modeling the anisotropy data at different concentrations allows for an accurate estimate of the number of water molecules in the hydration shell of OH(-), the reorientation dynamics of the OH(-) hydration complex, and the molecular-scale heat diffusivity.     

Vibrational response of hydrogen-bonded interfacial water is dominated by intramolecular coupling

Using the surface-specific vibrational technique of vibrational sum-frequency generation, we reveal that the double-peaked structure in the vibrational spectrum of hydrogen-bonded interfacial water molecules originates from vibrational coupling between the stretch and bending overtone, rather than from structural effects. This is demonstrated by isotopic dilution experiments, which reveal a smooth transition from two peaks to one peak, as D2O is converted into HDO. Our results show that the water interface is structurally more homogeneous than previously thought.     

Hydration strongly affects the molecular and electronic structure of membrane phospholipids

We investigate the structure and electronic properties of phosphatidylcholine (PC) under different degrees of hydration at the single-molecule and monolayer type level by linear scaling ab initio calculations. Upon hydration, the phospholipid undergoes drastic long-range conformational rearrangements which lead to a sickle-like ground-state shape. The structural unit of the tilted gel-phase PC appears to be a water-bridged PC dimer. We find that hydration dramatically alters the surface potential, dipole and quadrupole moments of the lipids and consequently guides the interactions of the lipids with other molecules and the communication between cells.     

Ultrafast vibrational and structural dynamics of the proton in liquid water

The dynamical behavior of excess protons in liquid water is investigated using femtosecond vibrational pump-probe spectroscopy. By resonantly exciting the O-H+-stretching mode of the H9O4(+) (Eigen) hydration structure of the proton and probing the subsequent absorption change over a broad frequency range, the dynamics of the proton is observed in real time. The lifetime of the protonic stretching mode is found to be approximately 120 fs, shorter than for any other vibration in liquid water. We also observe the interconversion between the H9O4(+) (Eigen) and H5O2(+) (Zundel) hydration structures of the proton. This interconversion, which constitutes an essential step of proton transport in water, is found to occur on an extremely fast (< 100 fs) time scale.     

The differential modulation of USP activity by internal regulatory domains, interactors and eight ubiquitin chain types

Ubiquitin-specific proteases (USPs) are papain-like isopeptidases with variable inter- and intramolecular regulatory domains. To understand the effect of these domains on USP activity, we have analyzed the enzyme kinetics of 12 USPs in the presence and absence of modulators using synthetic reagents. This revealed variations of several orders of magnitude in both the catalytic turnover (k_cat) and ubiquitin (Ub) binding (K_M) between USPs. Further activity modulation by intramolecular domains affects both the k_cat and K_M, whereas the intermolecular activators UAF1 and GMPS mainly increase the k_cat. Also, we provide the first comprehensive analysis comparing Ub chain preference. USPs can hydrolyze all linkages and show modest Ub-chain preferences, although some show a lack of activity toward linear di-Ub. This comprehensive kinetic analysis highlights the variability within the USP family.     

Purification of decorin core protein from human lung tissue

A chromatographic method to purify decorin core protein from human lung tissue is described. The method is simple and rapid, using a combination of two-anion exchange and one reversed phase chromatography steps and the enzymatic digestion with chondroitinase ABC. Approximately 170 microg decorin core protein were purified from 25 g of lung tissue with an enrichment factor of 1800-fold relative to the initial protein content. SDS-PAGE analysis of the final product revealed a single 42 kDa protein band, which was recognized by anti-decorin antibodies upon Western blotting and identified by mass spectrometry. Further digestion with PNGase F evidenced the presence of three N-linked oligosaccharides on the core protein. This method forms the basis for studying structural alterations of decorin related to the pathology of diseases where tissue destruction plays a role.     

DNP‐Supported Solid‐State NMR Spectroscopy of Proteins Inside Mammalian Cells

Elucidating at atomic level how proteins interact and are chemically modified in cells represents a leading frontier in structural biology. We have developed a tailored solid‐state NMR spectroscopic approach that allows studying protein structure inside human cells at atomic level under high‐sensitivity dynamic nuclear polarization (DNP) conditions. We demonstrate the method using ubiquitin (Ub), which is critically involved in cellular functioning. Our results pave the way for structural studies of larger proteins or protein complexes inside human cells, which have remained elusive to in‐cell solution‐state NMR spectroscopy due to molecular size limitations.