Crystal structure of CmABCB1 multi-drug exporter in lipidic mesophase revealed by LCP-SFX

CmABCB1 is a Cyanidioschyzon merolae homolog of human ABCB1, a well known ATP-binding cassette (ABC) transporter responsible for multi-drug resistance in various cancers. Three-dimensional structures of ABCB1 homologs have revealed the snapshots of inward- and outward-facing states of the transporters in action. However, sufficient information to establish the sequential movements of the open–close cycles of the alternating-access model is still lacking. Serial femtosecond crystallography (SFX) using X-ray free-electron lasers has proven its worth in determining novel structures and recording sequential conformational changes of proteins at room temperature, especially for medically important membrane proteins, but it has never been applied to ABC transporters. In this study, 7.7 monoacylglycerol with cholesterol as the host lipid was used and obtained well diffracting microcrystals of the 130 kDa CmABCB1 dimer. Successful SFX experiments were performed by adjusting the viscosity of the crystal suspension of the sponge phase with hydroxypropyl methylcellulose and using the high-viscosity sample injector for data collection at the SACLA beamline. An outward-facing structure of CmABCB1 at a maximum resolution of 2.22 Å is reported, determined by SFX experiments with crystals formed in the lipidic cubic phase (LCP-SFX), which has never been applied to ABC transporters. In the type I crystal, CmABCB1 dimers interact with adjacent molecules via not only the nucleotide-binding domains but also the transmembrane domains (TMDs); such an interaction was not observed in the previous type II crystal. Although most parts of the structure are similar to those in the previous type II structure, the substrate-exit region of the TMD adopts a different configuration in the type I structure. This difference between the two types of structures reflects the flexibility of the substrate-exit region of CmABCB1, which might be essential for the smooth release of various substrates from the transporter.

I know a dog when I see one: dogs (Canis familiaris) recognize dogs from videos

Several aspects of dogs’ visual and social cognition have been explored using bi-dimensional representations of other dogs. It remains unclear, however, if dogs do recognize as dogs the stimuli depicted in such representations, especially with regard to videos. To test this, 32 pet dogs took part in a cross-modal violation of expectancy experiment, during which dogs were shown videos of either a dog and that of an unfamiliar animal, paired with either the sound of a dog barking or of an unfamiliar vocalization. While stimuli were being presented, dogs paid higher attention to the exit region of the presentation area, when the visual stimulus represented a dog than when it represented an unfamiliar species. After exposure to the stimuli, dogs’ attention to different parts of the presentation area depended on the specific combination of visual and auditory stimuli. Of relevance, dogs paid less attention to the central part of the presentation area and more to the entrance area after being exposed to the barking and dog video pair, than when either was paired with an unfamiliar stimulus. These results indicate dogs were surprised by the latter pairings, not by the former, and were interested in where the barking and dog pair came from, implying recognition of the two stimuli as belonging to a conspecific. The study represents the first demonstration that dogs can recognize other conspecifics in videos.

Antecedent North Pacific Jet Regimes Conducive to the Development of Continental U.S. Extreme Temperature Events during the Cool Season

This study considers the development of continental U.S. extreme temperature events (ETEs) during the cool season (September–May), where extreme temperatures are defined in terms of percentiles and events are defined in terms of the spatial coverage of extreme temperatures. Following their identification, ETEs are classified into geographic clusters and stratified based on the state of the North Pacific jet (NPJ) stream prior to ETE initiation using an NPJ phase diagram. The NPJ phase diagram is developed from the two leading modes of NPJ variability during the cool season. The first mode corresponds to a zonal extension or retraction of the exit region of the climatological NPJ, while the second mode corresponds to a poleward or equatorward shift of the exit region of the climatological NPJ. The projection of 250-hPa zonal wind anomalies onto the NPJ phase diagram prior to ETEs demonstrates that the preferred state and evolution of the NPJ prior to ETEs varies considerably based on the geographic location of ETE initiation and the season. Southern plains extreme warm events are an exception, however, since extreme warm events in that location most frequently initiate following a retracted NPJ during all seasons. The NPJ phase diagram is subsequently utilized to examine a synoptic-scale flow evolution highly conducive to the initiation of southern plains extreme warm events via composite analysis. The composite analysis demonstrates that a retracted NPJ supports an amplification of the upper-tropospheric flow pattern over North America, which then induces persistent lower-tropospheric warm-air advection over the southern plains prior to ETE initiation.

The Development of the North Pacific Jet Phase Diagram as an Objective Tool to Monitor the State and Forecast Skill of the Upper-Tropospheric Flow Pattern

Previous studies employing empirical orthogonal function (EOF) analyses of upper-tropospheric zonal wind anomalies have identified the leading modes of North Pacific jet (NPJ) variability that prevail on synoptic time scales. The first mode corresponds to a zonal extension or retraction of the exit region of the climatological NPJ, while the second mode corresponds to a poleward or equatorward shift of the exit region of the climatological NPJ. These NPJ regimes can strongly influence the character of the large-scale flow pattern over North America. Consequently, knowledge of the prevailing NPJ regime and the forecast skill associated with each NPJ regime can add considerable value to operational medium-range (6–10-day) forecasts over North America. This study documents the development of an NPJ phase diagram, which is constructed from the two leading EOFs of 250-hPa zonal wind anomalies during 1979–2014 excluding the summer months (June–August). The projection of 250-hPa zonal wind anomalies at one or multiple times onto the NPJ phase diagram provides an objective characterization of the state or evolution of the upper-tropospheric flow pattern over the North Pacific with respect to the two leading EOFs. A 30-yr analysis of GEFS reforecasts with respect to the NPJ phase diagram demonstrates that forecasts verified during jet retraction and equatorward shift regimes are associated with significantly larger average errors than jet extension and poleward shift regimes. An examination of the best and worst forecasts further suggests that periods characterized by rapid NPJ regime transition and the development and maintenance of North Pacific blocking events exhibit reduced forecast skill.

Numerical simulation of gas–liquid flow behavior in the nozzle exit region of an effervescent atomizer

The pressure drop and particular geometric structure of the nozzle exit region of an effervescent atomizer cause complex changes in the flow pattern, which could affect the spray performance. In this study, the gas–liquid two-phase flow behavior in the nozzle exit region of the effervescent atomizer was investigated numerically. The results show that the flow behaviors in the nozzle exit region have disparate characteristics with different upstream flow regimes. For upstream churn flow, the liquid film morphology is closely related to fluctuation in the gas–liquid velocity, and the flow parameters (fluids’ velocities and gas void fraction) at the exit section vary regularly with time. For upstream bubbly flow, the instantaneous gas void fraction is determined by the bubble distribution inside the mixing chamber. The bubble will form a tadpole-like shape as a result of the complex flow field and the surface tension. The flow parameters at the exit section are in an oscillatory decay, and the fluctuation amplitude is larger than for churn flow. For upstream slug flow, the gas void fraction varies significantly with time. The discrete characteristic of the gas–liquid flow parameters at exit section is very obvious.

Synoptic Features Associated with Temporally Coherent Modes of Variability of the North Pacific Jet Stream

Time-extended EOF (TE-EOF) analysis is employed to examine the synoptic-scale evolution of the two leading modes of the North Pacific jet stream variability, namely, its zonal extension–retraction (TE-EOF 1) and the north–south shift of its exit region (TE-EOF 2). Use of the TE-EOF analysis enables a temporally coherent examination of the synoptic-scale evolution preceding and following peaks in each of the two leading modes that provides insight into the preferred evolutions of the North Pacific jet. Composite analyses are constructed based upon selecting peaks in the principal component time series of both phases of each TE-EOF whose magnitude exceeded 1.5 standard deviations. Jet extension events are associated with an anomalous cyclonic circulation over the Gulf of Alaska that induces a low-level warm anomaly over western North America. Jet retractions are associated with a nearly opposite configuration characterized by an anomalous anticyclonic circulation over the Aleutians and anomalous low-level cold anomaly over western North America. Similar but lower-amplitude upper-level patterns are noted in the composites of the corresponding poleward-/equatorward-shifted jet phases, with the poleward shift of the jet exit region tied to anomalously low geopotential heights over Alaska and anomalous low-level warmth over north-central North America. An equatorward shift of the exit region is tied to positive height anomalies over Alaska with downstream cold anomalies occurring in western North America. The more extreme downstream impacts that characterize TE-EOF 2 are also longer lasting (>5 days), suggesting potential utility in medium-range forecasts.