Advancing Health Equity in Community-Based Climate Action: From Concept to Practice.

Despite broad agreement that prioritizing health equity is critical to minimizing the health impacts of climate change, there is a lack of clarity about what advancing health equity means in practice. More than reducing health disparities; it also implies engaging and empowering marginalized communities. We propose a typology of health equity processes, focused on building community agency and power, and then apply it to a nonrepresentative, purposive sample of 48 community-based climate actions (CBCAs) selected from lists of projects funded by foundations and state climate programs and from other sources. All CBCAs were in the United States, community-based, active since 2015 or more recently, engaged in climate mitigation or adaptation, and stated health equity aims. Two team members reviewed project reports to assess the engagement of vulnerable and marginalized populations, agency-building, and transformation of community power relationships. Although 33 CBCAs reported efforts to build community agency, only 19 reported efforts to increase community power. City-led CBCAs showed less emphasis on agency-building and power transformation. This typology can support efforts to advance health equity by providing concrete indicators to diagnose gaps and track progress. (Am J Public Health. 2023;113(2):185-193. https://doi.org/10.2105/AJPH.2022.307143).

Structural analysis of the SRP Alu domain from Plasmodium falciparum reveals a non-canonical open conformation.

The eukaryotic signal recognition particle (SRP) contains an Alu domain, which docks into the factor binding site of translating ribosomes and confers translation retardation. The canonical Alu domain consists of the SRP9/14 protein heterodimer and a tRNA-like folded Alu RNA that adopts a strictly 'closed' conformation involving a loop-loop pseudoknot. Here, we study the structure of the Alu domain from Plasmodium falciparum (PfAlu), a divergent apicomplexan protozoan that causes human malaria. Using NMR, SAXS and cryo-EM analyses, we show that, in contrast to its prokaryotic and eukaryotic counterparts, the PfAlu domain adopts an 'open' Y-shaped conformation. We show that cytoplasmic P. falciparum ribosomes are non-discriminative and recognize both the open PfAlu and closed human Alu domains with nanomolar affinity. In contrast, human ribosomes do not provide high affinity binding sites for either of the Alu domains. Our analyses extend the structural database of Alu domains to the protozoan species and reveal species-specific differences in the recognition of SRP Alu domains by ribosomes.

Reconstitution of the human SRP system and quantitative and systematic analysis of its ribosome interactions.

Co-translational protein targeting to membranes depends on the regulated interaction of two ribonucleoprotein particles (RNPs): the ribosome and the signal recognition particle (SRP). Human SRP is composed of an SRP RNA and six proteins with the SRP GTPase SRP54 forming the targeting complex with the heterodimeric SRP receptor (SRαß) at the endoplasmic reticulum membrane. While detailed structural and functional data are available especially for the bacterial homologs, the analysis of human SRP was impeded by the unavailability of recombinant SRP. Here, we describe the large-scale production of all human SRP components and the reconstitution of homogeneous SRP and SR complexes. Binding to human ribosomes is determined by microscale thermophoresis for individual components, assembly intermediates and entire SRP, and binding affinities are correlated with structural information available for all ribosomal contacts. We show that SRP RNA does not bind to the ribosome, while SRP binds with nanomolar affinity involving a two-step mechanism of the key-player SRP54. Ultrasensitive binding of SRP68/72 indicates avidity by multiple binding sites that are dominated by the C-terminus of SRP72. Our data extend the experimental basis to understand the mechanistic principles of co-translational targeting in mammals and may guide analyses of complex RNP-RNP interactions in general.

The Escherichia coli SRP Receptor Forms a Homodimer at the Membrane.

The Escherichia coli signal recognition particle (SRP) receptor, FtsY, plays a fundamental role in co-translational targeting of membrane proteins via the SRP pathway. Efficient targeting relies on membrane interaction of FtsY and heterodimerization with the SRP protein Ffh, which is driven by detachment of α helix (αN1) in FtsY. Here we show that apart from the heterodimer, FtsY forms a nucleotide-dependent homodimer on the membrane, and upon αN1 removal also in solution. Homodimerization triggers reciprocal stimulation of GTP hydrolysis and occurs in vivo. Biochemical characterization together with integrative modeling suggests that the homodimer employs the same interface as the heterodimer. Structure determination of FtsY NG+1 with GMPPNP shows that a dimerization-induced conformational switch of the γ-phosphate is conserved in Escherichia coli, filling an important gap in SRP GTPase activation. Our findings add to the current understanding of SRP GTPases and may challenge previous studies that did not consider homodimerization of FtsY.

Structural Basis for Conserved Regulation and Adaptation of the Signal Recognition Particle Targeting Complex.

The signal recognition particle (SRP) is a ribonucleoprotein complex with a key role in targeting and insertion of membrane proteins. The two SRP GTPases, SRP54 (Ffh in bacteria) and FtsY (SRα in eukaryotes), form the core of the targeting complex (TC) regulating the SRP cycle. The architecture of the TC and its stimulation by RNA has been described for the bacterial SRP system while this information is lacking for other domains of life. Here, we present the crystal structures of the GTPase heterodimers of archaeal (Sulfolobus solfataricus), eukaryotic (Homo sapiens), and chloroplast (Arabidopsis thaliana) SRP systems. The comprehensive structural comparison combined with Brownian dynamics simulations of TC formation allows for the description of the general blueprint and of specific adaptations of the quasi-symmetric heterodimer. Our work defines conserved external nucleotide-binding sites for SRP GTPase activation by RNA. Structural analyses of the GDP-bound, post-hydrolysis states reveal a conserved, magnesium-sensitive switch within the I-box. Overall, we provide a general model for SRP cycle regulation by RNA.

Symportin 1 chaperones 5S RNP assembly during ribosome biogenesis by occupying an essential rRNA-binding site.

During 60S biogenesis, mature 5S RNP consisting of 5S RNA, RpL5 and RpL11, assembles into a pre-60S particle, where docking relies on RpL11 interacting with helix 84 (H84) of the 25S RNA. How 5S RNP is assembled for recruitment into the pre-60S is not known. Here we report the crystal structure of a ternary symportin Syo1-RpL5-N-RpL11 complex and provide biochemical and structural insights into 5S RNP assembly. Syo1 guards the 25S RNA-binding surface on RpL11 and competes with H84 for binding. Pull-down experiments show that H84 releases RpL11 from the ternary complex, but not in the presence of 5S RNA. Crosslinking mass spectrometry visualizes structural rearrangements on incorporation of 5S RNA into the Syo1-RpL5-RpL11 complex supporting the formation of a pre-5S RNP. Our data underline the dual role of Syo1 in ribosomal protein transport and as an assembly platform for 5S RNP.

The Los Angeles County Community Disaster Resilience Project - a community-level, public health initiative to build community disaster resilience.

Public health officials need evidence-based methods for improving community disaster resilience and strategies for measuring results. This methods paper describes how one public health department is addressing this problem. This paper provides a detailed description of the theoretical rationale, intervention design and novel evaluation of the Los Angeles County Community Disaster Resilience Project (LACCDR), a public health program for increasing community disaster resilience. The LACCDR Project utilizes a pretest-posttest method with control group design. Sixteen communities in Los Angeles County were selected and randomly assigned to the experimental community resilience group or the comparison group. Community coalitions in the experimental group receive training from a public health nurse trained in community resilience in a toolkit developed for the project. The toolkit is grounded in theory and uses multiple components to address education, community engagement, community and individual self-sufficiency, and partnerships among community organizations and governmental agencies. The comparison communities receive training in traditional disaster preparedness topics of disaster supplies and emergency communication plans. Outcome indicators include longitudinal changes in inter-organizational linkages among community organizations, community member responses in table-top exercises, and changes in household level community resilience behaviors and attitudes. The LACCDR Project is a significant opportunity and effort to operationalize and meaningfully measure factors and strategies to increase community resilience. This paper is intended to provide public health and academic researchers with new tools to conduct their community resilience programs and evaluation research. Results are not yet available and will be presented in future reports.

Structural insights into the assembly of the human and archaeal signal recognition particles.

The signal recognition particle (SRP) is a conserved ribonucleoprotein (RNP) complex that co-translationally targets membrane and secretory proteins to membranes. The assembly of the particle depends on the proper folding of the SRP RNA, which in mammalia and archaea involves an induced-fit mechanism within helices 6 and 8 in the S domain of SRP. The two helices are juxtaposed and clamped together upon binding of the SRP19 protein to their apices. In the current assembly paradigm, archaeal SRP19 causes the asymmetric loop of helix 8 to bulge out and expose the binding platform for the key player SRP54. Based on a heterologous archaeal SRP19-human SRP RNA structure, mammalian SRP19 was thought not to be able to induce this change, thus explaining the different requirements of SRP19 for SRP54 recruitment. In contrast, the crystal structures of a crenarchaeal and the all-human SRP19-SRP RNA binary complexes presented here show that the asymmetric loop is bulged out in both binary complexes. Differences in SRP assembly between mammalia and archaea are therefore independent of SRP19 and are based on differences in SRP RNA itself. A new SRP-assembly scheme is presented.

The structure of the mammalian signal recognition particle (SRP) receptor as prototype for the interaction of small GTPases with Longin domains.

The eukaryotic signal recognition particle (SRP) and its receptor (SR) play a central role in co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum. The SR is a heterodimeric complex assembled by the two GTPases SRalpha and SRbeta, which is membrane-anchored. Here we present the 2.45-A structure of mammalian SRbeta in its Mg2+ GTP-bound state in complex with the minimal binding domain of SRalpha termed SRX. SRbeta is a member of the Ras-GTPase superfamily closely related to Arf and Sar1, while SRX belongs to the SNARE-like superfamily with a fold also known as longin domain. SRX binds to the P loop and the switch regions of SRbeta-GTP. The binding mode and structural similarity with other GTPase-effector complexes suggests a co-GAP (GTPase-activating protein) function for SRX. Comparison with the homologous yeast structure and other longin domains reveals a conserved adjustable hydrophobic surface within SRX which is of central importance for the SRbeta-GTP:SRX interface. A helix swap in SRX results in the formation of a dimer in the crystal structure. Based on structural conservation we present the SRbeta-GTP:SRX structure as a prototype for conserved interactions in a variety of GTPase regulated targeting events occurring at endomembranes.

Structural analysis of the human Golgi-associated plant pathogenesis related protein GAPR-1 implicates dimerization as a regulatory mechanism.

The plant pathogenesis related proteins group 1 (PR-1) and a variety of related mammalian proteins constitute a PR-1 protein family that share sequence and structural similarities. GAPR-1 is a unique family member as thus far it is the only PR-1 family member that is not co-translationally targeted to the lumen of the endoplasmic reticulum before trafficking to either vacuoles or secretion. Here we report that GAPR-1 may form dimers in vitro and in vivo, as determined by yeast two-hybrid screening, biochemical and biophysical assays. The 1.55A crystal structure demonstrates that GAPR-1 is structurally homologous to the other PR-1 family members previously solved (p14a and Ves V 5). Through an examination of inter-molecular interactions between GAPR-1 molecules in the crystal lattice, we propose a number of the highly conserved amino acid residues of the PR-1 family to be involved in the regulation of dimer formation of GAPR-1 with potential implications for other PR-1 family members. We show that mutagenesis of these conserved amino acid residues leads to a greatly increased dimer population. A recent report suggests that PR-1 family members may exhibit serine protease activity and further examination of the dimer interface of GAPR-1 indicates that a catalytic triad similar to that of serine proteases may be formed across the dimer interface by residues from both molecules within the dimer.

Crystallization of a Golgi-associated PR-1-related protein (GAPR-1) that localizes to lipid-enriched microdomains.

The human Golgi-associated PR-1-related protein (GAPR-1) is closely related to plant pathogenesis-related (PR-1) proteins, which are upregulated in response to pathogen attack. Family members have been identified in a variety of organisms, together constituting the superfamily of PR-1 proteins. GAPR-1 is found within lipid-enriched microdomains on the cytosolic side of the endomembrane system. GAPR-1 is tightly anchored to membranes and absent from the cytosol, although it does not possess a membrane-spanning domain. Crystals of recombinantly expressed GAPR-1 have been grown that diffract to high (1.5 A) resolution. Complete data sets have been collected on a trigonal crystal form (P3(1)21/P3(2)21), with unit-cell parameters a = b = 73.5, c = 63.2 A. Molecular replacement using the NMR coordinates of tomato pathogenesis-related protein (28% identity) was unsuccessful and a search for heavy-metal derivatives or alternative phasing methods has been initiated.