The crystal structure and insight into the substrate specificity of the α-L rhamnosidase RHA-P from Novosphingobium sp. PP1Y.

Flavonoid natural products are well known for their beneficial antimicrobial, antitumor, and anti-inflammatory properties, however, some of these natural products often are rhamnosylated, which severely limits their bioavailability. The lack of endogenous rhamnosidases in the human GI tract not only prevents many of these glycosylated compounds from being of value in functional foods but also limits the modification of natural product libraries being tested for drug discovery. RHA-P is a catalytically efficient, thermostable α-l-rhamnosidase from the marine bacterium Novosphingobium sp. PP1Y that selectively hydrolyzes α-1,6 and α-1,2 glycosidic linkages between a terminal rhamnose and a flavonoid moiety. This work reports the 2.2 Šresolution crystal structure of RHA-P, which is an essential step forward in the characterization of RHA-P as a potential catalyst to increase the bioavailability of rhamnosylated natural compounds. The structure shows highly conserved rhamnose- and calcium-binding residues in a shallow active site that is housed in the (ß/α)8 domain. In comparison to BT0986 (pdbID: 5MQN), the only known structure of an RHA-P homolog, the morphology, electrostatic potentials and amino acid composition of the substrate binding pocket are significantly different, offering insight into the substrate preference of RHA-P for glycosylated aryl compounds such as hesperidin, naringin, rutin, and quercitrin, over polysaccharides, which are preferred by BT0986. These preferences were further explored by using in silico docking, the results of which are consistent with the known kinetic data for RHA-P acting on different rhamnosylated flavonoids. Due to its promiscuity, relative thermostability compared to other known rhamnosidases, and catalytic efficiency even in significant concentrations of organic solvents, RHA-P continues to show potential for biocatalytic applications.

Popular education to improve water quality and hygiene in a Mexican indigenous community.

Long-term research has identified significant water contamination and associated poor health outcomes in the indigenous community of Alpuyeca, located in south-central Mexico. We set out to develop a popular education initiative in this community to improve water, sanitation and hygiene (WaSH) knowledge and practices. In order to avoid recreating hierarchical power dynamics in this vulnerable community, a participatory action research (PAR) design was used, wherein the community took leadership and facilitation roles in each stage of the research process. In qualitative interviews and design sessions, community members identified unsatisfied WaSH needs in households and community institutions and articulated a clear worldview of the spiritual role of water, which guided the development of a series of popular education-based workshops and discussions. The popular education initiative process was documented with a mixed methods framework, using before-and-after surveys, semi-structured interviews and participatory observation. Increases in knowledge and practices related to water purification, water consumption and hand hygiene were noted in the community. The community identified locally installed and managed ecotechnologies as a key opportunity for sustainable development, community participation and the adoption of water and sanitation systems, compatible with public imaginaries of the role of water.

Deported, homeless, and into the canal: Environmental structural violence in the binational Tijuana River.

INTRODUCTION: The US deports more Mexicans to Tijuana than any other borderland city. Returning involuntarily as members of a stigmatized underclass, many find themselves homeless and de-facto stateless. Subject to routinized police victimization, many take refuge in the Tijuana River Canal (El Bordo). Previous reports suggest Tijuana River water may be contaminated but prior studies have not accessed the health effects or contamination of the water closest to the river residents. METHODS: A binational, transdisciplinary team undertook a socio-environmental, mixed methods assessment to simultaneously characterize Tijuana River water quality with chemical testing, assess the frequency of El Bordo residents' water-related diseases, and trace water contacts with epidemiological survey methods (n = 85 adults, 18+) in 2019, and ethnographic methods in 2019-2021. Our analysis brings the structural violence framework into conversation with an environmental injustice perspective to documented how social forces drive poor health outcomes enacted through the environment. RESULTS: The Tijuana River water most proximate to its human inhabitants fails numerous water-quality standards, posing acute health risks. Escherichia coli values were ∼40,000 times the Mexican regulatory standard for directly contacted water. Skin infections (47%), dehydration (40%) and diarrhea (28%) were commonly reported among El Bordo residents. Residents are aware the water is contaminated and strive to minimize harm to their health by differentially using local water sources. Their numerous survival constraints, however, are exacerbated by routine police violence which propels residents and other people who inject drugs into involuntary contact with contaminated water. DISCUSSION: Human rights to drinking water, sanitation and hygiene are routinely violated among El Bordo inhabitants. This is exacerbated by violent policing practices that force unhoused deportees to seek refuge in waterways, and drive water contacts. Furthermore, US-Mexico 'free-trade' agreements drive rapid growth in Tijuana, restrict Mexican environmental regulation enforcement, and drive underinvestment in sewage systems and infrastructure.