Structure and activation mechanism of the rice Salt Overly Sensitive 1 (SOS1) Na+/H+ antiporter.

Salinity is one of the most severe abiotic stresses that adversely affect plant growth and agricultural productivity. The plant Na+/H+ antiporter Salt Overly Sensitive 1 (SOS1) located in the plasma membrane extrudes excess Na+ out of cells in response to salt stress and confers salt tolerance. However, the molecular mechanism underlying SOS1 activation remains largely elusive. Here we elucidate two cryo-electron microscopy structures of rice (Oryza sativa) SOS1, a full-length protein in an auto-inhibited state and a truncated version in an active state. The SOS1 forms a dimeric architecture, with an NhaA-folded transmembrane domain portion in the membrane and an elongated cytosolic portion of multiple regulatory domains in the cytoplasm. The structural comparison shows that SOS1 adopts an elevator transport mechanism accompanied by a conformational transition of the highly conserved Pro148 in the unwound transmembrane helix 5 (TM5), switching from an occluded conformation in the auto-inhibited state to a conducting conformation in the active state. These findings allow us to propose an inhibition-release mechanism for SOS1 activation and elucidate how SOS1 controls Na+ homeostasis in response to salt stress.

Immunization with recombinant Erns-LTB fusion protein elicits protective immune responses against bovine viral diarrhea virus.

Bovine viral diarrhea virus (BVDV), a major infectious pathogen and is associated with major economic losses and significant impact on animal welfare worldwide. Here, recombinant Erns-LTB protein vaccine containing MF59 adjuvant was prepared and assessed using a mouse model. The recombinant plasmid (pET32a-Erns-LTB) was constructed and transformed into BL21 (DE3) cells to produce Erns-LTB protein. The Erns-LTB protein was formulated with MF59 adjuvant, when delivered intraperitoneally in mice, exhibited higher immunogenic and induced superior levels of anti-BVDV IgG compared with the MF59 adjuvanted Erns protein. Importantly, after challenged with different BVDV BJ175170 and BJ1305 isolate strains, mice inoculated with Erns-LTB protein displayed alleviated pathological damage and decreased plasma virus shedding compared with mice inoculated with Erns protein. The enhanced protection from Erns-LTB protein is mediated by T cell immunity and primarily based on CD4+ T helper (Th) and CD8+ cytotoxic T lymphocyte (CTL), these results suggest that Erns-LTB protein has potential to protect against a broad range of BVDV strains thereby providing a novel direction for developing broadly protective vaccines.