Calcium homeostasis modulator 1 (CALHM1) is a voltage-gated ATP release channel that plays an important role in neural gustatory signaling and the pathogenesis of Alzheimer’s disease. Here, we present a cryo–electron microscopy structure of full-length Ca2+-free CALHM1 from Danio rerio at an overall resolution of 3.1 Å. Our structure reveals an octameric architecture with a wide pore diameter of ~20 Å, presumably representing the active conformation. The overall structure is substantially different from that of the isoform CALHM2, which forms both undecameric hemichannels and gap junctions. The N-terminal small helix folds back to the pore and forms an antiparallel interaction with transmembrane helix 1. Structural analysis revealed that the extracellular loop 1 region within the dimer interface may contribute to oligomeric assembly. A positive potential belt inside the pore was identified that may modulate ion permeation. Our structure offers insights into the assembly and gating mechanism of the CALHM1 channel.

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As an essential element of crop growth, phosphorus (P) plays an important role in maintaining agricultural sustainability and ecological balance. A quantitative understanding of agronomic and environmental soil P thresholds at the global scale is required to enhance P-use efficiency and crop productivity while preventing environmental P losses. To address this issue, we conducted a meta-analysis with 584 data observations from 175 studies in 326 locations to assess the critical soil P thresholds as related to crop type and soil properties. The results showed that the average agronomic soil P threshold across all crops was 19.36 mg•kg −1 and the threshold was highest for vegetables (mean = 30.04 mg•kg −1 ), intermediate for cereals (mean = 17.06 mg•kg −1 ), and lowest for legumes (mean = 9.30 mg•kg −1 ). In contrast, the mean environmental soil P threshold across soil textures was 48.56 mg•kg −1 . The environmental soil P threshold was significantly affected by soil texture and followed the order of clay > loam > sandy soils. Agronomic soil P thresholds correlated negatively with climate variables including mean annual temperature and mean annual precipitation, and positively with soil organic matter content. The environmental P thresholds correlated negatively with soil pH. Gradient-boosted regression tree statistical model analysis suggested that crop type and soil texture were the most important determinants of the variation in agronomic and environmental soil P thresholds, respectively. This study provides a first quantitative assessment of agronomic and environmental soil P thresholds for different crops, climates, and soil textures and should help improve the management of cropland P worldwide.

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