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The temperature dependence of the backbone motions in Escherichia coli ribonuclease HI was studied on multiple time scales by 15N nuclear magnetic spin relaxation. Laboratory frame relaxation data at 285, 300, and 310 K were analyzed using the model-free and reduced spectral density approaches. The temperature dependence of the order parameters was used to define a characteristic temperature for the motions of the backbone N-H bond vectors on picosecond to nanosecond time scales. The characteristic temperatures for secondary structure elements, loops, and the C-terminus are approximately 1000, approximately 300, and approximately 170 K, respectively. The observed variation in the characteristic temperature indicates that the energy landscape, and thus the configurational heat capacity, is markedly structure dependent in the folded protein. The effective correlation times for internal motions do not show significant temperature dependence. Conformational exchange was observed for a large number of residues forming a contiguous region of the protein that includes the coiled coil formed by helices alpha A and alpha D. Exchange broadening in the CPMG experiments decreased with increased temperature, directly demonstrating that the microscopic exchange rate is faster than the pulse repetition rate of 1.2 ms. The temperature dependence of the exchange contributions to the transverse relaxation rate constant shows approximately Arrhenius behavior over the studied temperature range with apparent activation enthalpies of approximately 20-50 kJ/mol. Numerical calculations suggest that these values underestimate the activation barriers by at most a factor of 2. The present results obtained at 300 K are compared to those reported previously [Mandel, A. M., Akke, M., & Palmer, A. G., III (1995) J. Mol. Biol. 246, 144-163] to establish the reproducibility of the experimental techniques.

IMPORTANCEAssociations between in utero exposure to maternal SARS-CoV-2 infection and neurodevelopment are speculated, but currently unknown.OBJECTIVE To examine the associations between maternal SARS-CoV-2 infection during pregnancy, being born during the COVID-19 pandemic regardless of maternal SARS-CoV-2 status, and neurodevelopment at age 6 months. DESIGN, SETTING, AND PARTICIPANTSA cohort of infants exposed to maternal SARS-CoV-2 infection during pregnancy and unexposed controls was enrolled in the COVID-19 Mother Baby Outcomes Initiative at Columbia University Irving Medical Center in New York City. All women who delivered at Columbia University Irving Medical Center with a SARS-CoV-2 infection during pregnancy were approached. Women with unexposed infants were approached based on similar gestational age at birth, date of birth, sex, and mode of delivery. Neurodevelopment was assessed using the Ages & Stages Questionnaire, 3rd Edition (ASQ-3) at age 6 months. A historical cohort of infants born before the pandemic who had completed the 6-month ASQ-3 were included in secondary analyses.EXPOSURES Maternal SARS-CoV-2 infection during pregnancy and birth during the COVID-19 pandemic. MAIN OUTCOMES AND MEASURESOutcomes were scores on the 5 ASQ-3 subdomains, with the hypothesis that maternal SARS-CoV-2 infection during pregnancy would be associated with decrements in social and motor development at age 6 months. RESULTSOf 1706 women approached, 596 enrolled; 385 women were invited to a 6-month assessment, of whom 272 (70.6%) completed the ASQ-3. Data were available for 255 infants enrolled in the COVID-19 Mother Baby Outcomes Initiative (114 in utero exposed, 141 unexposed to SARS-CoV-2; median maternal age at delivery, 32.0 [IQR, 19.0-45.0] years). Data were also available from a historical cohort of 62 infants born before the pandemic. In utero exposure to maternal SARS-CoV-2 infection was not associated with significant differences on any ASQ-3 subdomain, regardless of infection timing or severity. However, compared with the historical cohort, infants born during the pandemic had significantly lower scores on gross motor

Model-free parameters obtained from nuclear magnetic resonance (NMR) relaxation experiments and molecular dynamics (MD) simulations commonly are used to describe the intramolecular dynamical properties of proteins. To assess the relative accuracy and precision of experimental and simulated model-free parameters, three independent data sets derived from backbone 15N NMR relaxation experiments and two independent data sets derived from MD simulations of Escherichia-coli ribonuclease HI are compared. The widths of the distributions of the differences between the order parameters for pairs of NMR data sets are congruent with the uncertainties derived from statistical analyses of individual data sets; thus, current protocols for analyzing NMR data encapsulate random uncertainties appropriately. Large differences in order parameters for certain residues are attributed to systematic differences between samples for intralaboratory comparisons and unknown, possibly magnetic field-dependent, experimental effects for interlaboratory comparisons. The widths of distributions of the differences between the order parameters for two NMR sets are similar to widths of distributions for an NMR and an MD set or for two MD sets. The linear correlations between the order parameters for an MD set and an NMR set are within the range of correlations observed between pairs of NMR sets. These comparisons suggest that the NMR and MD generalized order parameters for the backbone amide N-H bond vectors are of comparable accuracy for residues exhibiting motions on a fast time scale (< 100 ps). Large discrepancies between NMR and MD order parameters for certain residues are attributed to the occurrence of "rare" motional events over the simulation trajectories, the disruption of an element of secondary structure in one of the simulations, and lack of consensus among the experimental data sets. Consequently, (easily detectable) severe distortions of local protein structure and infrequent motional events in MD simulations appear to be the most serious artifacts affecting the accuracy and precision, respectively, of MD order parameters relative to NMR values. In addition, MD order parameters for motions on a fast (< 100 ps) timescale are more precisely determined than their NMR counterparts, thereby permitting more detailed dynamic characterization of biologically important residues by MD simulation than is sometimes possible by experimental methods. Proteins 28:481-493, 1997.

The mediators of tissue damage in systemic lupus erythematosus (SLE) such as antibodies, cytokines and activated immune cells have direct access to most organs in the body but must penetrate the blood-brain barrier (BBB) to gain access to brain tissue. We hypothesized that compromise of the BBB occurs episodically such that the brain will acquire tissue damage slowly and not at the same rate as other organs. On the basis of these assumptions, we wished to determine if duration of disease correlated with brain injury, as measured with functional magnetic resonance imaging (fMRI), and if this was independent of degree of tissue damage in other organs. We investigated differences in brain activation patterns using fMRI in 13 SLE patients stratified by disease duration of ≤2 years (short-term [ST]) or ≥10 years (long-term [LT]). Two fMRI paradigms were selected to measure working memory and emotional response (fearful faces task). Performance in the working memory task was significantly better in the ST group for one and two shape recall; however, both groups did poorly with three shape recall. Imaging studies demonstrated significantly increased cortical activation in the ST group in regions associated with cognition during the two shape retention phase of the working memory task (P < 0.001) and increased amygdala (P < 0.05) and superior parietal (P < 0.01) activation in response to the fearful faces paradigm. In conclusion, analysis of activation patterns stratified by performance accuracy, differences in comorbid disease, corticosteroid doses or disease activity suggests that these observed differences are attributable to SLE effects on the central nervous system exclusive of vascular disease or other confounding influences. Our hypothesis is further supported by the lack of correlation between regional brain abnormalities on fMRI and the Systemic Lupus International Collaborating Clinics (SLICC) damage index.