Why we need a European focus on foodborne parasites.

Foodborne parasites (FBP) are recognized as being a neglected pathogen group, often associated with marginalized or disadvantaged populations, especially those living in regions where water supply or sanitation are inadequate. Nevertheless, we are also increasingly recognising that FBP are not just restricted to such places, and even those that do have a circumscribed endemic area may also travel further in our globalised world; FBP are relevant everywhere, including Europe. Against this background, COST Action Euro-FBP (FA1408) was established and ran for a period of 4 years, addressing a number of different questions related to FBP, particularly in the European setting. In this special issue (SI), some of the issues and outputs associated with Euro-FBP are considered in greater depth, as an output also of the final Euro-FBP meeting. As well as more general issues regarding, for example, globalization and climate change, use of economic models, and the value of risk-based surveillance that puts the topic in perspective, individual articles are included that address specific parasites. These include protozoan parasites, such as Cryptosporidium, Giardia, and Toxoplasma, as contaminants of water, shellfish, and fresh produce, fishborne parasites such as Anisakid nematodes, and meatborne parasites, such as Trichinella. Some of the works provide specific data on occurrence or outbreaks, whilst others are concerned with techniques. In addition, implementation of some of the educational and collaborative tools that are unique to COST Actions are described. COST Actions are not generally intended to deliver a scientific endpoint, and Euro-FBP does not do so. However, the articles in this SI, along with other articles published elsewhere during and subsequent to the course of the Action, as direct outputs of the Euro-FBP activities, indicate that FBP are indeed a relevant topic for European scientists.

Bacteriophages Isolated from Chicken Meat and the Horizontal Transfer of Antimicrobial Resistance Genes.

Antimicrobial resistance in microbes poses a global and increasing threat to public health. The horizontal transfer of antimicrobial resistance genes was thought to be due largely to conjugative plasmids or transposons, with only a minor part being played by transduction through bacteriophages. However, whole-genome sequencing has recently shown that the latter mechanism could be highly important in the exchange of antimicrobial resistance genes between microorganisms and environments. The transfer of antimicrobial resistance genes by phages could underlie the origin of resistant bacteria found in food. We show that chicken meat carries a number of phages capable of transferring antimicrobial resistance. Of 243 phages randomly isolated from chicken meat, about a quarter (24.7%) were able to transduce resistance to one or more of the five antimicrobials tested into Escherichia coli ATCC 13706 (DSM 12242). Resistance to kanamycin was transduced the most often, followed by that to chloramphenicol, with four phages transducing tetracycline resistance and three transducing ampicillin resistance. Phages able to transduce antimicrobial resistance were isolated from 44% of the samples of chicken meat that we tested. The statistically significant (P = 0.01) relationship between the presence of phages transducing kanamycin resistance and E. coli isolates resistant to this antibiotic suggests that transduction may be an important mechanism for transferring kanamycin resistance to E. coli. It appears that the transduction of resistance to certain antimicrobials, e.g., kanamycin, not only is widely distributed in E. coli isolates found on meat but also could represent a major mechanism for resistance transfer. The result is of high importance for animal and human health.

The C-terminal cavity of the Na,K-ATPase analyzed by docking and electrophysiology.

The Na,K-ATPase is essential to all animals, since it maintains the electrochemical gradients that energize the plasma membrane. Naturally occurring inhibitors of the pump from plants have been used pharmaceutically in cardiac treatment for centuries. The inhibitors block the pump by binding on its extracellular side and thereby locking it. To explore the possibilities for designing an alternative way of targeting the pump function, we have examined the structural requirements for binding to a pocket that accommodates the two C-terminal residues, YY, in the crystal structures of the pump. To cover the sample space of two residues, we first performed docking studies with the 400 possible dipeptides. For validation of the in silico predictions, pumps with 13 dipeptide sequences replacing the C-terminal YY were expressed in Xenopus laevis oocytes and examined with electrophysiology. Our data show a significant correlation between the docking scores from two different methods and the experimentally determined sodium affinities, which strengthens the previous hypothesis that sodium binding is coupled to docking of the C-terminus. From the dipeptides that dock the best and better than wild-type YY, it may therefore be possible to develop specific drugs targeting a previously unexplored binding pocket in the sodium pump.

Shelf-life extension of vacuum-packaged meat from pheasant (Phasianus colchicus) by lactic acid treatment.

We investigated the influence of lactic acid treatment of pheasant meat before vacuum-packaged storage of 3, 7, and 10 d at +6°C on microbiota and pH. Breast muscle samples were collected from carcasses of slaughtered as well as from hunted (shot) wild pheasants. Immersion of meat samples in 3% (wt/wt) lactic acid for 60 s effectuated a significant drop in pH of approximately 0.5 to 0.7 units, which remained during the entire storage period. In parallel, total aerobic counts of such treated and stored samples were on an average 1.5 to 1.7 log units lower than in non-acid-treated samples. Similar results were found for Enterobacteriaceae. A significant decrease in pH was measured at d 7 and 10 in the acid-treated samples in comparison with the untreated ones. In summary, the immersion of pheasant breast meat cuts in dilute lactic acid significantly reduced microbiota during vacuum-packed storage, even at slight temperature abuse conditions.

Preventing Microbial Growth in Game Meat by Applying Polyphenolic Extracts from Olive Mill Vegetation Water.

We studied the efficacy of different formulations of polyphenol extracts (mainly containing hydroxytyrosol and tyrosol) from olive mill vegetation water on the microflora on the surfaces of game meat cuts with high or low initial bacterial loads. Meat with a high microbial load (>5 Log cfu/g; mean value = 6.83 ± 0.45 standard deviation) was immersed for 10 or 60 sec into 25% and 10% solutions of microencapsulated freeze-dried and non-encapsulated polyphenolic extracts. Aerobic colony, Enterobacteriaceae, Pseudomonas spp., and lactic acid bacteria counts were determined on treated samples compared to controls after 7 days of storage (in vacuum-packed conditions at +3 °C). Significant differences were registered only for aerobic colony count for a 10% liquid extract treatment (0.64 log reduction). In contrast, the dipping or immersion of game meat with low initial microbial loads (<5 Log cfu/g; mean value = 3.58 ± 0.72 standard deviation) in 10% solutions of the polyphenol extracts effectuated significant reductions in all bacteria counts (p < 0.002) at 7 and 14 days of storage for different extracts, independently from the application methods. The use of the extracts to inhibit bacterial growth in game meat should only be considered if a good hygienic baseline is guaranteed.

Detection of Extended Spectrum ß-Lactamase-Producing Escherichia coli with Biofilm Formation from Chicken Meat in Istanbul.

Antimicrobial resistance is one of the major public health problems worldwide. This study aimed to detect the presence of extended-spectrum ß-lactamase-(ESBL-)producing Escherichia (E.) coli in chicken meat in Istanbul, Türkiye. Raw chicken meat samples (n = 208) were collected from different sale points and analyzed for ESBL-producing E. coli. In total, 101 (48.5%) isolates were confirmed as E. coli by PCR, of which 80/101 (79.2%) demonstrated multiple antibiotic resistance. Resistance against amoxicillin-clavulanic acid was most frequent (87.1%). Eighteen isolates (17.8%) demonstrated phenotypical ESBL resistance, as assessed by the double disc synergy test (DDST). Isolates were tested for the presence of ß-lactamase genes and mobilized colistin-resistant genes. The blaTEM group was most frequently detected (97.02%), followed by blaCTX m (45.5%), blaSHV (9.9%), and blaOXA-2 (0.9%). However, mcr genes and blaNDM,blaKPC, blaVIM, and blaOXA-48 genes were not found in any isolate. E. coli strains were tested for biofilm formation in six different media [Nutrient broth, LB broth, Tryptone Soya broth (TSB), TSB containing 1% sucrose, TSB containing 0.6% yeast extract, and BHI]. Biofilm formation by E. coli isolates (44/101, 43.5%) was highest in TSB with 1% sucrose. It is worth noting that all biofilm-producing isolates were found to harbor the blaTEM-1 gene, which can indicate a high level of antibiotic resistance. This is the first report about ESBL-producing E. coli in poultry meat, the exposure of consumers in Istanbul metropolitan areas, and the ability of E. coli from this region to produce biofilms.

Salmonella in Wild Boar Meat: Prevalence and Risk Assessment in Central Italy (Umbria and Marche Region).

A survey was conducted from 2018 to 2023 to assess the presence of Salmonella in 280 hunted wild boar (carcasses after evisceration and skinning, N = 226; liver, N = 258; and fecal samples, N = 174). The overall prevalence was 2.86% (confidence interval 95%, 1.45-5.45%) with five positive samples detected in carcasses, three in the liver, and one in a fecal sample. This prevalence was in line with those found in nearby areas denoting a low number of positive samples. Positive animals were over 24 months of age and weighed, before skinning, 59.00 ± 9.11 Kg and no difference was detected in microbial loads between samples positive and negative for Salmonella (aerobic colony count of 4.59 and 4.66 log CFU/400 cm2, and Enterobacteriaceae count of 2.89 and 2.73 log CFU/400 cm2 (mean values) in positive and negative subjects, respectively). Salmonella Stanleyville was the most frequently isolated serotype. A semiquantitative risk assessment was conducted for the first time in game meat considering two products, meat cuts intended for cooking and fermented dry sausages. Only proper cooking can reduce the risk of ingestion of Salmonella to the minimum for consumers, whereas ready-to-eat dry sausages constitute risk products in terms of foodborne Salmonellosis (risk score of 64 out of 100).

Transmission Scenarios of Listeria monocytogenes on Small Ruminant On-Farm Dairies.

Listeria monocytogenes can cause severe foodborne infections in humans and invasive diseases in different animal species, especially in small ruminants. Infection of sheep and goats can occur via contaminated feed or through the teat canal. Both infection pathways result in direct (e.g., raw milk from an infected udder or fresh cheese produced from such milk) or indirect exposure of consumers. The majority of dairy farmers produces a high-risk product, namely fresh cheese made from raw ewe's and goat's milk. This, and the fact that L. monocytogenes has an extraordinary viability, poses a significant challenge to on-farm dairies. Yet, surprisingly, almost no scientific studies have been conducted dealing with the hygiene and food safety aspects of directly marketed dairy products. L. monocytogenes prevalence studies on small ruminant on-farm dairies are especially limited. Therefore, it was our aim to focus on three main transmission scenarios of this important major foodborne pathogen: (i) the impact of caprine and ovine listerial mastitis; (ii) the significance of clinical listeriosis and outbreak scenarios; and (iii) the impact of farm management and feeding practices.

Changes in Flavor and Volatile Composition of Meat and Meat Products Observed after Exposure to Atmospheric Pressure Cold Plasma (ACP).

Studies on the atmospheric pressure cold plasma (ACP) exposure of meat and meat products mainly determine microbial inactivation, lipid oxidation, and meat color. Some studies include sensory evaluation, but only a few determine the changes in volatile composition due to ACP treatment. The results of sensory evaluation are inconclusive and range from "improvement" to "off-odor". This could be due to differences in the food matrix, especially in processed foods, or different experimental settings, including inadvertent effects such as sample heating. The few studies analyzing volatile composition report changes in alcohols, esters, aldehydes, and other compounds, but not necessarily changes that are novel for meat and meat products. Most studies do not actually measure the formation of reactive species, although this is needed to determine the exact reactions taking place in the meat during ACP treatment. This is a prerequisite for an adjustment of the plasma conditions to achieve antimicrobial effects without compromising sensory quality. Likewise, such knowledge is necessary to clarify if ACP-exposed meat and products thereof require regulatory approval.

Presence of Foodborne Bacteria in Wild Boar and Wild Boar Meat-A Literature Survey for the Period 2012-2022.

The wild boar is an abundant game species with high reproduction rates. The management of the wild boar population by hunting contributes to the meat supply and can help to avoid a spillover of transmissible animal diseases to domestic pigs, thus compromising food security. By the same token, wild boar can carry foodborne zoonotic pathogens, impacting food safety. We reviewed literature from 2012-2022 on biological hazards, which are considered in European Union legislation and in international standards on animal health. We identified 15 viral, 10 bacterial, and 5 parasitic agents and selected those nine bacteria that are zoonotic and can be transmitted to humans via food. The prevalence of Campylobacter, Listeria monocytogenes, Salmonella, Shiga toxin-producing E. coli, and Yersinia enterocolitica on muscle surfaces or in muscle tissues of wild boar varied from 0 to ca. 70%. One experimental study reported the transmission and survival of Mycobacterium on wild boar meat. Brucella, Coxiella burnetii, Listeria monocytogenes, and Mycobacteria have been isolated from the liver and spleen. For Brucella, studies stressed the occupational exposure risk, but no indication of meat-borne transmission was evident. Furthermore, the transmission of C. burnetii is most likely via vectors (i.e., ticks). In the absence of more detailed data for the European Union, it is advisable to focus on the efficacy of current game meat inspection and food safety management systems.

Microflora, Contents of Polyamines, Biogenic Amines, and TVB-N in Bovine Offal and Game Meat for the Raw-Feeding of Adult Dogs.

Microflora and contents of biogenic amines/polyamines and total volatile basic nitrogen (TVB-N) in 99 samples of bovine offal (red offal, n = 41 and other offal and mixes, n = 45) and wild game meat (n = 13) for raw meat-based diets (RMBD) for dogs were analyzed. Samples were bought in 11 local pet food shops and in one game-handling establishment in Austria (Lower Austria, Styria, and Vienna) in September and October 2022. Median contents (first and third quartiles in brackets) of cadaverine, histamine, tyramine, spermidine, and spermine were 20.7 [16.7; 28.6]; 25.4 [17.1; 47.2]; 18.9 [13.6; 38.9]; 15.2 [11.2; 21.2]; and 41.9 [50 mg/kg in 85.9% of samples, indicating the use of low-quality ingredients or inappropriate storage conditions. However, only 10.1% of samples were determined to be not compliant with a maximum amine content proposed for pet food. Median contents of the total aerobic bacteria counts (TACs), Pseudomonas, and Enterobacteriaceae were 7.4 [6.4; 8.0]; 6.5 [5.5; 7.7]; and 4.8 [3.9; 5.6] log CFU/g, respectively, with significantly lower counts in red offal RMBD (p < 0.05). TVB-N exceeded 150 mg/kg in 87.9% of samples. The TACs and Enterobacteriaceae numbers in red offal RMBD were comparable to those in food-grade red offal after 6 days of aerobic storage at 7 °C, i.e., temperatures higher than required for food-grade offal, but acceptable for animal by-products intended for RMBD production. In 80.8% of samples, numbers of Enterobacteriaceae exceeded the EU legal limit. From 12 of these samples, Salmonellae was able to be isolated, with counts from 0.03 MPN/g to 110 MPN/g. Salmonella enterica ser. Montevideo (n = 3), and S. enterica ser. Give and S. enterica ssp. Diarizonae (n = 2 each) were the most frequently isolated, while Listeria monocytogenes was rarely recovered (2%). Whilst exposure of humans handling such pet food can be reduced by hygiene precautions, the risk remains that dogs can acquire a feed-borne salmonellosis and shed the pathogen.

Monitoring of Paenibacillus larvae in Lower Austria through DNA-Based Detection without De-Sporulation: 2018 to 2022.

American foulbrood is caused by the spore-forming Paenibacillus larvae. Although the disease effects honey bee larvae, it threatens the entire colony. Clinical signs of the disease are seen at a very late stage of the disease and bee colonies are often beyond saving. Therefore, through active monitoring based on screening, an infection can be detected early and bee colonies can be protected with hygiene measures. As a result, the pressure to spread in an area remains low. The cultural and molecular biological detection of P. larvae is usually preceded by spore germination before detection. In this study, we compared the results of two methods, the culture detection and RT-PCR detection of DNA directly isolated from spores. Samples of honey and cells with honey surrounding the brood were used in a five-year voluntary monitoring program in a western part of Lower Austria. DNA-extraction from spores to speed up detection involved one chemical and two enzymatic steps before mechanical bashing-beat separation and additional lysis. The results are comparable to culture-based methods, but with a large time advantage. Within the voluntary monitoring program, the proportion of bee colonies without the detection of P. larvae was high (2018: 91.9%, 2019: 72.09%, 2020: 74.6%, 2021: 81.35%, 2022: 84.5%), and in most P. larvae-positive bee colonies, only a very low spore content was detected. Nevertheless, two bee colonies in one apiary with clinical signs of disease had to be eradicated.

Treatment of Ready-To-Eat Cooked Meat Products with Cold Atmospheric Plasma to Inactivate Listeria and Escherichia coli.

Ready-to-eat meat products have been identified as a potential vehicle for Listeria monocytogenes. Postprocessing contamination (i.e., handling during portioning and packaging) can occur, and subsequent cold storage together with a demand for products with long shelf life can create a hazardous scenario. Good hygienic practice is augmented by intervention measures in controlling post-processing contamination. Among these interventions, the application of 'cold atmospheric plasma' (CAP) has gained interest. The reactive plasma species exert some antibacterial effect, but can also alter the food matrix. We studied the effect of CAP generated from air in a surface barrier discharge system (power densities 0.48 and 0.67 W/cm2) with an electrode-sample distance of 15 mm on sliced, cured, cooked ham and sausage (two brands each), veal pie, and calf liver pâté. Colour of samples was tested immediately before and after CAP exposure. CAP exposure for 5 min effectuated only minor colour changes (ΔE max. 2.7), due to a decrease in redness (a*), and in some cases, an increase in b*. A second set of samples was contaminated with Listeria (L.) monocytogenes, L. innocua and E. coli and then exposed to CAP for 5 min. In cooked cured meats, CAP was more effective in inactivating E. coli (1 to 3 log cycles) than Listeria (from 0.2 to max. 1.5 log cycles). In (non-cured) veal pie and calf liver pâté that had been stored 24 h after CAP exposure, numbers of E. coli were not significantly reduced. Levels of Listeria were significantly reduced in veal pie that had been stored for 24 h (at a level of ca. 0.5 log cycles), but not in calf liver pâté. Antibacterial activity differed between but also within sample types, which requires further studies.

Characterisation of Listeria monocytogenes Isolates from Hunted Game and Game Meat from Finland.

Listeria monocytogenes is an important foodborne zoonotic bacterium. It is a heterogeneous species that can be classified into lineages, serogroups, clonal complexes, and sequence types. Only scarce information exists on the properties of L. monocytogenes from game and game meat. We characterised 75 L. monocytogenes isolates from various game sources found in Finland between 2012 and 2020. The genetic diversity, presence of virulence and antimicrobial genes were studied with whole genome sequencing. Most (89%) of the isolates belonged to phylogenetic lineage (Lin) II and serogroup (SG) IIa. SGs IVb (8%) and IIb (3%) of Lin I were sporadically identified. In total, 18 clonal complexes and 21 sequence types (STs) were obtained. The most frequent STs were ST451 (21%), ST585 (12%) and ST37 (11%) found in different sample types between 2012 and 2020. We observed 10 clusters, formed by closely related isolates with 0-10 allelic differences. Most (79%) of the virulence genes were found in all of the L. monocytogenes isolates. Only fosX and lin were found out of 46 antimicrobial resistance genes. Our results demonstrate that potentially virulent and antimicrobial-sensitive L. monocytogenes isolates associated with human listeriosis are commonly found in hunted game and game meat in Finland.

Treatment of Fresh Meat, Fish and Products Thereof with Cold Atmospheric Plasma to Inactivate Microbial Pathogens and Extend Shelf Life.

Assuring the safety of muscle foods and seafood is based on prerequisites and specific measures targeted against defined hazards. This concept is augmented by 'interventions', which are chemical or physical treatments, not genuinely part of the production process, but rather implemented in the framework of a safety assurance system. The present paper focuses on 'Cold Atmospheric pressure Plasma' (CAP) as an emerging non-thermal intervention for microbial decontamination. Over the past decade, a vast number of studies have explored the antimicrobial potential of different CAP systems against a plethora of different foodborne microorganisms. This contribution aims at providing a comprehensive reference and appraisal of the latest literature in the area, with a specific focus on the use of CAP for the treatment of fresh meat, fish and associated products to inactivate microbial pathogens and extend shelf life. Aspects such as changes to organoleptic and nutritional value alongside other matrix effects are considered, so as to provide the reader with a clear insight into the advantages and disadvantages of CAP-based decontamination strategies.

Cysteine residues are responsible for the sulfurous off-flavor formed in heated whey protein solutions.

Odor-active volatile sulfur compounds are formed in heated food protein systems. In the present study, hydrogen sulfide (H2S) was found to be the most abundant sulfur volatile in whey protein solutions (whey protein isolate [WPI], a whey model system and single whey proteins) by gas chromatography-flame photometric detector (GC-FPD) analysis after heat treatments (60-90 °C for 10 min, 90 °C for 120 min and UHT-like treatment). H2S was detected in WPI after heating at 90 °C for 10 min, and was significantly increased at higher heat load (90 °C for 120 min and the UHT-like treatment). Site-specific LC-MS/MS-based proteomic analysis was conducted, monitoring desulfurization reactions in these protein systems to investigate the mechanism of H2S formation in heated WPI. Cysteine residues from beta-lactoglobulin were found to be responsible for the formation of H2S in heated WPI, presumably via beta-elimination.

Slaughter of Pregnant Cattle at an Austrian Abattoir: Prevalence and Gestational Age.

The slaughter of pregnant cattle raises ethical-moral questions with regard to animal welfare, but also concerns of consumers because of higher levels of sex steroids in the meat from pregnant cattle. Since no data on the slaughter of pregnant cattle in Austria were available, we examined uteri of slaughtered female cattle in one Austrian mid-size abattoir. Sample size was calculated for an assumed prevalence of 2.5% (±1%; 95% confidence interval) of cows or heifers slaughtered in the last trimester of pregnancy and amounted to 870 cows and 744 heifers. 1633 female cattle of domestic origin were examined, most of them of dual-purpose type. Pregnancy was detected in 30/759 heifers and in 74/874 cows (an overall prevalence of 6.4%). The number of cattle in the last trimester of pregnancy was 16 to 26, depending on the evaluation scheme. We found no significant differences in percentages of pregnant cattle sent to slaughter for beef, dual-purpose and dairy breeds, although the latter group demonstrated the lowest percentage. Our results are comparable with those from previously conducted studies in other member states of the European Union. Measures to avoid sending pregnant cattle to slaughter should be implemented at farm-level.

Contents of Polyamines and Biogenic Amines in Canned Pet (Dogs and Cats) Food on the Austrian Market.

Biogenic amines accumulate in proteinaceous raw materials used for pet food production. In canned, sterilized food, amine levels of the ingredients are preserved and may both be indicative of hygiene deficiencies in the ingredients as well as for potential adverse effects to the animals feeding on it. We determined the contents of biogenic amines and polyamines (dansyl derivatives, high performance liquid chromatography) in a variety of canned food for dogs (n = 72) and cats (n = 114) on the Austrian market and compared the results with common quality indices. Contents of putrescine, cadaverine, and tyramine were below the limit of detection in >70% of samples (maximum values: 21.5, 98.4 and 32.5 mg/kg wet weight, respectively). Median contents of histamine, spermidine, and spermine were 14.5, 12.7, and 29.4 mg/kg, and maximum values were 61.6, 28.2, and 53.6 mg/kg wet weight, respectively. The sum of (putrescine + cadaverine + histamine + tyramine) was >50 mg/kg in 22.6% of samples. The biogenic amine index exceeded "1" in 26.7% of samples. Whilst cat food contained significantly higher amounts of tyramine, dog food contained significantly higher amounts of histamine and spermine. In canned cat food, the ingredient "fish" was identified as a statistically significant risk factor for a biogenic amine index > 1 (relative risk = 3.0 (95% confidence interval: 1.8-5.5)) and for (putrescine + cadaverine + histamine + tyramine) exceeding 50 mg/kg (relative risk = 2.4 (95% confidence interval: 1.2-4.6)), due to higher contents of cadaverine in food samples containing fish. While all samples met the limits suggested in pet food production, we could demonstrate that the inclusion of fish in the formulation bears a significant risk for higher cadaverine contents.

Molecular mechanism of sugar transport in plants unveiled by structures of glucose/H+ symporter STP10.

Sugars are essential sources of energy and carbon and also function as key signalling molecules in plants. Sugar transport proteins (STP) are proton-coupled symporters responsible for uptake of glucose from the apoplast into plant cells. They are integral to organ development in symplastically isolated tissues such as seed, pollen and fruit. Additionally, STPs play a vital role in plant responses to stressors such as dehydration and prevalent fungal infections like rust and mildew. Here we present a structure of Arabidopsis thaliana STP10 in the inward-open conformation at 2.6 Å resolution and a structure of the outward-occluded conformation at improved 1.8 Å resolution, both with glucose and protons bound. The two structures describe key states in the STP transport cycle. Together with molecular dynamics simulations that establish protonation states and biochemical analysis, they pinpoint structural elements, conserved in all STPs, that clarify the basis of proton-to-glucose coupling. These results advance our understanding of monosaccharide uptake, which is essential for plant organ development, and set the stage for bioengineering strategies in crops.

Structural comparison of GLUT1 to GLUT3 reveal transport regulation mechanism in sugar porter family.

The human glucose transporters GLUT1 and GLUT3 have a central role in glucose uptake as canonical members of the Sugar Porter (SP) family. GLUT1 and GLUT3 share a fully conserved substrate-binding site with identical substrate coordination, but differ significantly in transport affinity in line with their physiological function. Here, we present a 2.4 Å crystal structure of GLUT1 in an inward open conformation and compare it with GLUT3 using both structural and functional data. Our work shows that interactions between a cytosolic "SP motif" and a conserved "A motif" stabilize the outward conformational state and increases substrate apparent affinity. Furthermore, we identify a previously undescribed Cl- ion site in GLUT1 and an endofacial lipid/glucose binding site which modulate GLUT kinetics. The results provide a possible explanation for the difference between GLUT1 and GLUT3 glucose affinity, imply a general model for the kinetic regulation in GLUTs and suggest a physiological function for the defining SP sequence motif in the SP family.