Transcription with a laser: Radiation-damage-free diffraction of RNA Polymerase II crystals

Well-diffracting crystals are essential to obtain relevant structural data that will lead to understanding of RNA Polymerase II (Pol II) transcriptional processes at a molecular level. Here we present a strategy to study Pol II crystals using negative stain transmission electron microscopy (TEM) and a methodology to optimize radiation damage free data collection using free electron laser (FEL) at the Linac Coherent Light Source (LCLS). The use of negative stain TEM allowed visualization and optimization of crystal diffraction by monitoring the lattice quality of crystallization conditions. Nano crystals bearing perfect lattices were seeded and used to grow larger crystals for FEL data collection. Moreover, the use of in house designed crystal loops together with ultra-violet (UV) microscopy for crystal detection facilitated data collection. Such strategy permitted collection of multiple crystals of radiation-free-damage data, resulting in the highest resolution of wild type (WT) Pol II crystals ever observed.

MicroED Structure of Au146(p-MBA)57 at Subatomic Resolution Reveals a Twinned FCC Cluster

Solving the atomic structure of metallic clusters is fundamental to understanding their optical, electronic, and chemical properties. Herein we present the structure of the largest aqueous gold cluster, Au146(p-MBA)57 (p-MBA: para-mercaptobenzoic acid), solved by electron micro-diffraction (MicroED) to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The 146 gold atoms may be decomposed into two constituent sets consisting of 119 core and 27 peripheral atoms. The core atoms are organized in a twinned FCC structure, whereas the surface gold atoms follow a C2 rotational symmetry about an axis bisecting the twinning plane. The protective layer of 57 p-MBAs fully encloses the cluster and comprises bridging, monomeric, and dimeric staple motifs. Au146(p-MBA)57 is the largest cluster observed exhibiting a bulk-like FCC structure as well as the smallest gold particle exhibiting a stacking fault.

Transmission electron microscopy for the evaluation and optimization of crystal growth

The crystallization of protein samples remains the most significant challenge in structure determination by X-ray crystallography. Here, the effectiveness of transmission electron microscopy (TEM) analysis to aid in the crystallization of biological macromolecules is demonstrated. It was found that the presence of well ordered lattices with higher order Bragg spots, revealed by Fourier analysis of TEM images, is a good predictor of diffraction-quality crystals. Moreover, the use of TEM allowed (i) comparison of lattice quality among crystals from different conditions in crystallization screens; (ii) the detection of crystal pathologies that could contribute to poor X-ray diffraction, including crystal lattice defects, anisotropic diffraction and crystal contamination by heavy protein aggregates and nanocrystal nuclei; (iii) the qualitative estimation of crystal solvent content to explore the effect of lattice dehydration on diffraction and (iv) the selection of high-quality crystal fragments for microseeding experiments to generate reproducibly larger sized crystals. Applications to X-ray free-electron laser (XFEL) and micro-electron diffraction (microED) experiments are also discussed.

Structural Basis for the Interconversion of Maltodextrins by MalQ, the Amylomaltase of Escherichia coli

Amylomaltase MalQ is essential for the metabolism of maltose and maltodextrins in Escherichia coli. It catalyzes transglycosylation/disproportionation reactions in which glycosyl or dextrinyl units are transferred among linear maltodextrins of various lengths. To elucidate the molecular basis of transglycosylation by MalQ, we have determined three crystal structures of this enzyme, i.e. the apo-form, its complex with maltose, and an inhibitor complex with the transition state analog acarviosine-glucose-acarbose, at resolutions down to 2.1 Å. MalQ represents the first example of a mesophilic bacterial amylomaltase with known structure and exhibits an N-terminal extension of about 140 residues, in contrast with previously described thermophilic enzymes. This moiety seems unique to amylomaltases from Enterobacteriaceae and folds into two distinct subdomains that associate with different parts of the catalytic core. Intriguingly, the three MalQ crystal structures appear to correspond to distinct states of this enzyme, revealing considerable conformational changes during the catalytic cycle. In particular, the inhibitor complex highlights the requirement of both a 3-OH group and a 4-OH group (or α1-4-glycosidic bond) at the acceptor subsite +1 for the catalytically competent orientation of the acid/base catalyst Glu-496. Using an HPLC-based MalQ enzyme assay, we could demonstrate that the equilibrium concentration of maltodextrin products depends on the length of the initial substrate; with increasing numbers of glycosidic bonds, less glucose is formed. Thus, both structural and enzymatic data are consistent with the extremely low hydrolysis rates observed for amylomaltases and underline the importance of MalQ for the metabolism of maltodextrins in E. coli.

Understanding the experience of pain in terminally ill patients

BACKGROUND

Terminally ill patients commonly experience substantial pain. Unresolved pain has been cited as evidence that end-of-life care is of poor quality. However, the data on which that conclusion is based are limited. We aimed to provide additional data on the experience of pain in such patients.

METHODS

We interviewed 988 terminally ill patients from six randomly selected US sites. We asked them who had treated their pain in the previous 4 weeks (primary-care physician, pain specialist, or both), and whether they wanted more pain medication than they were receiving, or why they did not want more.

FINDINGS

496 (50%) terminally ill patients reported moderate or severe pain. 514 (52%) individuals had seen a primary-care physician for treatment of pain in the previous 4 weeks and 198 (20%) saw a pain specialist. Of those who had been treated by their primary-care physician, 287 (29%) wanted more therapy, 613 (62%) wanted their pain therapy to remain the same, and 89 (9%) wanted to reduce or stop their pain therapy. Several reasons for not wanting additional therapy were offered-fear of addiction, dislike of mental or physical side-effects, and not wanting to take more pills or injections. We saw no association between disease and amount of pain between disease and the desire for more treatment. Black patients were more likely to seek additional pain therapy, see a pain specialist, and refuse additional medication because of fear of addiction than other populations.

INTERPRETATION

Although half of terminally ill patients experienced moderate to severe pain, only 30% of them wanted additional pain treatment from their primary-care physician. The number of patients experiencing pain remains too high. However, the number is not as large as perceived. Additionally, most are willing to tolerate pain. Furthermore, the experience of pain is constant across major terminal diseases.

Humanities in medical education: revisiting the doctor-patient relationship

Medical students, overwhelmed by new information, rarely appreciate patients' complaints beyond their biomedical aspects. To encourage students to think more comprehensively about patients, I initiated a biweekly series of seminars in medical humanities at the Duke University School of Medicine. Emphasizing science, without acknowledging the importance of the humanities, undermines the essential attribute of the good physician: the ability to establish a productive dialogue with the patient. Education in the humanities can broaden the student's scientific perspective, and reinforce medicine's critical, interpretive, and interpersonal tasks. The humanities inculcate a tolerance for ambiguity, provide a basis for the reconciliation of competing values, and foster the ability to discern the narrative thread in the setting of illness. The paper highlights the elements of the lecture series and suggests how it helps cultivate a core competency of medical education: learning to engage in the dialogue that grounds the doctor-patient relationship.

Neonatal osteomyelitis examined by bone scintigraphy

Thirty-three infants less than six weeks of age and suspected of having osteomyelitis were examined by bone scintigraphy. Each of the 25 sites of proved osteomyelitis in 15 individuals demonstrated abnormal radionuclide localization. Ten additional scintigraphically positive but radiographically normal sites were detected. Optimal quality scintigrams of the growth plate complex and osteomyelitis in neonates appeared similar to those in older children. All neonates suspected of having osteomyelitis should be studied with bone scintigraphy following initial radiographs.