Ultrafast anisotropic protein quake propagation after CO photodissociation in myoglobin.

"Protein quake" denotes the dissipation of excess energy across a protein, in response to a local perturbation such as the breaking of a chemical bond or the absorption of a photon. Femtosecond time-resolved small- and wide-angle X-ray scattering (TR-SWAXS) is capable of tracking such ultrafast protein dynamics. However, because the structural interpretation of the experiments is complicated, a molecular picture of protein quakes has remained elusive. In addition, new questions arose from recent TR-SWAXS data that were interpreted as underdamped oscillations of an entire protein, thus challenging the long-standing concept of overdamped global protein dynamics. Based on molecular-dynamics simulations, we present a detailed molecular movie of the protein quake after carbon monoxide (CO) photodissociation in myoglobin. The simulations suggest that the protein quake is characterized by a single pressure peak that propagates anisotropically within 500 fs across the protein and further into the solvent. By computing TR-SWAXS patterns from the simulations, we could interpret features in the reciprocal-space SWAXS signals as specific real-space dynamics, such as CO displacement and pressure wave propagation. Remarkably, we found that the small-angle data primarily detect modulations of the solvent density but not oscillations of the bare protein, thereby reconciling recent TR-SWAXS experiments with the notion of overdamped global protein dynamics.

Anisotropic time-resolved solution X-ray scattering patterns from explicit-solvent molecular dynamics.

Time-resolved wide-angle X-ray scattering (TR-WAXS) is an emerging experimental technique used to track chemical reactions and conformational transitions of proteins in real time. Thanks to increased time resolution of the method, anisotropic TR-WAXS patterns were recently reported, which contain more structural information than isotropic patterns. So far, however, no method has been available to compute anisotropic WAXS patterns of biomolecules, thus limiting the structural interpretation. Here, we present a method to compute anisotropic TR-WAXS patterns from molecular dynamics simulations. The calculations accurately account for scattering of the hydration layer and for thermal fluctuations. For many photo-excitable proteins, given a low intensity of the excitation laser, the anisotropic pattern is described by two independent components: (i) an isotropic component, corresponding to common isotropic WAXS experiments and (ii) an anisotropic component depending on the orientation of the excitation dipole of the solute. We present a set of relations for the calculation of these two components from experimental scattering patterns. Notably, the isotropic component is not obtained by a uniform azimuthal average on the detector. The calculations are illustrated and validated by computing anisotropic WAXS patterns of a spheroidal protein model and of photoactive yellow protein. Effects due to saturated excitation at high intensities of the excitation laser are discussed, including opportunities to extract additional structural information by modulating the laser intensity.

Variability of forces applied by experienced physiotherapists during provocation of the sacroiliac joint.

OBJECTIVE: To evaluate the distribution of total force vector and force components intended for the right and left sacroiliac joint, respectively, during pain-provocation sacroiliac joint tests. DESIGN: Two force plates, each capable of sensing three orthogonal forces, were used in a descriptive study to assess force. BACKGROUND: Studies evaluating the reliability of sacroiliac joint tests have revealed conflicting results and to our knowledge, no studies have evaluated the distribution of forces and their variations. METHODS: Fifteen physiotherapists, experienced in musculoskeletal therapy, performed the distraction test and pressure on apex sacralis on the same healthy person on two occasions. RESULTS: In both tests, the total force vector was less on the force plate closer to the physiotherapist. The vertical force component dominated and was considerably greater than the lateral (examined person supine/prone). The caudal/cranial force component was small. Systematic differences were found for the total force vector and for the lateral and vertical force components between occasions and/or between the force plates. CONCLUSIONS: The consistency of total force vector and force components was incomplete within and between physiotherapists and between occasions. Relevance. The results indicate that forces have to be investigated as the questions still arise of whether the variation in force distribution has any importance in pain response, whether force registration could be a useful pain evaluation instrument, and whether force registration could be a step towards standardising pain-provocation sacroiliac joint tests.

Reproducibility of manual pressure force on provocation of the sacroiliac joint.

BACKGROUND AND PURPOSE: Previous studies of pain-provocation sacroiliac (SI) joint tests have revealed conflicting results. The aim of the present study was to evaluate the intra- and inter-test reliability of pressure force applied during distraction test, compression test and pressure on the apex sacralis. METHODS: Seventeen physiotherapists (PTs), median age 43 years and median clinical experience 11 years, all experienced in musculoskeletal evaluation and therapy, participated in the study. Each PT performed each test on the same healthy volunteer for 20 s, on three separate occasions, at intervals of one week using a specially constructed examination table which registered pressure force. RESULTS: The PTs were capable of maintaining a relatively constant pressure force for 20 s. The intra-test reliability was acceptable even though there were individual differences on different occasions between those PTs who used the SI joint tests often and those who seldom or never used them. The inter-test reliability was insufficient. CONCLUSIONS: The findings indicate the advantage of registering pressure force as a complement for standardized methods for pain-provoking tests and when learning provocation tests, since individual variability was considerable.

Lithium attenuates hypokinesia induced by immobilization stress in rats.

1. Hypokinesia following immobilization stress in rats is attenuated by anti-depressant drugs used in the treatment of unipolar depression. Lithium has anti-depressant effects both clinically and in other animal models of depression, but the mechanism of its anti-depressant effect has not been elucidated. 2. To determine if lithium reverses immobilization-induced hypokinesia, the effects of lithium and immobilization stress were tested in a fully factorial 2 x 2 design. 3. Half the rats were fed chronic dietary lithium, while the other half ate regular chow. Half of each group were exposed to one hour immobilization, while the other half remained in their home cages until the test. Activity was measured for 20 min in an automated activity meter. 4. Stress significantly reduced activity, but a significant interaction between stress and lithium was found, indicating that lithium attenuated the effect of stress. 5. Lithium-induced attenuation of immobilization stress may serve as an animal model for the anti-depressant effects of lithium.

Myo-inositol attenuates the enhancement of the serotonin syndrome by lithium.

Lithium elicits opposite effects on two behavioural syndromes in rats: enhancement of the 5-HT1A-linked serotonin syndrome and attenuation of the 5-HT2-linked wet dog shakes. The ability of intracerebroventricular (ICV) myo-inositol or forskolin to reverse the enhancement of the serotonin syndrome by lithium was tested in rats that were fed chronic dietary lithium or control diet and injected with the serotonin agonist 5-MeODMT (5-methoxy-N, N-dimethyltryptamine). Lithium enhanced the total serotonin syndrome score and particularly flat posture and tremor. Inositol, but not forskolin, mitigated the effects of lithium. Inositol was also injected in the lateral ventricle of rats pretreated with chronic dietary lithium or regular rat chow for 3 weeks and injected with carbidopa and L-5-hydroxytryptophan (5-HTP). Lithium attenuated wet dog shakes, but inositol had no significant effect on lithium-treated or control rats. These findings suggest that the enhancement of the serotonin syndrome by lithium may be related to lithium-induced inositol depletion.