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Tripartite ATP-independent periplasmic (TRAP) transporters are secondary-active transporters that receive their substrates via a soluble-binding protein to move bioorganic acids across bacterial or archaeal cell membranes. Recent cryo-electron microscopy (cryo-EM) structures of TRAP transporters provide a broad framework to understand how they work, but the mechanistic details of transport are not yet defined. Here we report the cryo-EM structure of the Haemophilus influenzae N-acetylneuraminate TRAP transporter (HiSiaQM) at 2.99 Å resolution (extending to 2.2 Å at the core), revealing new features. The improved resolution (the previous HiSiaQM structure is 4.7 Å resolution) permits accurate assignment of two Na+ sites and the architecture of the substrate-binding site, consistent with mutagenic and functional data. Moreover, rather than a monomer, the HiSiaQM structure is a homodimer. We observe lipids at the dimer interface, as well as a lipid trapped within the fusion that links the SiaQ and SiaM subunits. We show that the affinity (KD) for the complex between the soluble HiSiaP protein and HiSiaQM is in the micromolar range and that a related SiaP can bind HiSiaQM. This work provides key data that enhances our understanding of the ‘elevator-with-an-operator’ mechanism of TRAP transporters.

We test common sense psychology of intragroup relations whereby people assume that intragroup respect and ingroup prototypicality are positively related. In Study 1a, participants rated a group member as more prototypical if they learned that group member was highly respected rather than disrespected. In Study 1b, participants rated a group member as more respected by other group members if they learned that group member was prototypical rather than unprototypical. As a commonsense psychology of groups, we reasoned that the perceived relationship between prototypicality and intragroup respect would be stronger for cohesive groups compared to incohesive groups. The effect of intragroup respect on perceptions of prototypicality (Study 2a & 2c) and the effect of prototypicality on perceptions of intragroup respect (Study 2b) were generally stronger for participants considering cohesive groups relative to incohesive groups. However, the interaction effect of prototypicality and group cohesion on intragroup respect did fail to replicate in Study 2d. In Studies 3, 4a, and 4b we manipulated the relationship between prototypicality and intragroup respect and found that when these variables were in perceptual harmony participants perceived groups as more cohesive. The results of eight out of nine studies conducted are consistent with the prediction that people make inferences about intragroup respect, prototypicality, and group cohesion in a manner that maintains perceptual harmony.

We examined environmental activist behaviour as a function of two different forms of environmental identity: identification with nature (i.e., seeing oneself as part of nature, more often referred to as connectedness to nature) and politicized environmental identity (i.e., seeing oneself as a part of a collective struggle to protect the environment). We extend prior work that found politicized environmental identity mediates a relationship between identification with nature and self-reports of environmental activism (Schmitt, Mackay, et al., 2019) by using observed behavioural indicators of environmental activism: taking pro-environmental buttons (Study 1), donating to an environmental organization (Study 2), or writing pro-environmental letters to politicians (Study 3). In Study 2 the relationship between identification with nature and activist behaviour was fully mediated by politicized environmental identity. In Studies 1 and 3, politicized environmental identity partially mediated a relationship between identification with nature and observed activist behaviour. We estimated the mean effect size of the mediation pathways in all three studies using meta-analysis, which supported the mediation model.

Supporters of the Confederate battle flag often argue that their support is driven by pride in the South, not negative racial attitudes. Opponents of the Confederate battle flag often argue that the flag represents racism, and that support for the flag is an expression of racism and an attempt to maintain oppression of Blacks in the Southern United States. We evaluate these two competing views in explaining attitudes toward the Confederate battle flag in the Southern United States through a survey of 526 Southerners. In the aggregate, our latent variable model suggests that White support for the flag is driven by Southern pride, political conservatism, and blatant negative racial attitudes toward Blacks. Using cluster-analysis we were able to distinguish four distinct sub-groups of White Southerners: Cosmopolitans, New Southerners, Traditionalists, and Supremacists. The greatest support for the Confederate battle flag is seen among Traditionalists and Supremacists; however, Traditionalists do not display blatant negative racial attitudes toward Blacks, while Supremacists do. Traditionalists make up the majority of Confederate battle flag supporters in our sample, weakening the claim that supporters of the flag are generally being driven by negative racial attitudes toward Blacks.

Bacteria and archaea use tripartite ATP-independent periplasmic (TRAP) transporters to import essential nutrients. Davies et al. report a high resolution structure of a TRAP and show that it uses an ‘elevator-with-an operator’ mechanism.

Multicomponent transporters are used by bacteria to transport a wide range of nutrients. These systems use a substrate-binding protein to bind the nutrient with high affinity and then deliver it to a membrane-bound transporter for uptake. Nutrient uptake pathways are linked to the colonisation potential and pathogenicity of bacteria in humans and may be candidates for antimicrobial targeting. Here we review current research into bacterial multicomponent transport systems, with an emphasis on the interaction at the membrane, as well as new perspectives on the role of lipids and higher oligomers in these complex systems.