Gdt1, Gdt2 and the P-type ATPase Pmr1 regulate divalent cations (Ca²⁺ and Mn²⁺) in the fission yeast Schizosaccharomyces pombe

In eukaryotes, calcium (Ca²⁺) and manganese (Mn²⁺) ion homeostasis in the early secretory pathway is crucial for protein glycosylation, cell wall biosynthesis, and cell structure. To clarify the roles of the UPF0016 family proteins Gdt1 and Gdt2 in the regulation of divalent cations, we performed genetic and phenotypic analyses on single-gene deletion mutants (Δ gdt1 , Δ gdt2 and Δ pmr1 ) and double-gene deletion mutants in Schizosaccharomyces pombe . In the presence of CaCl₂ and MnCl₂, Δ gdt1 cells exhibit marked hypersensitivity, indicating that Gdt1 is a major contributor to divalent cation regulation; in contrast, Δ gdt2 and Δ pmr1 mutants show only mild growth defects. However, the combined deletion of gdt1 or gdt2 with pmr1 results in a strong synthetic growth phenotype, suggesting that Gdt1, Gdt2, and Pmr1 play complementary roles in maintaining divalent cation regulation within the secretory network. Structural comparative analysis reveals that Gdt1 retains a conserved five-transmembrane structure, whereas Gdt2 adopts a six-transmembrane conformation. Both proteins preserve the EIGDKT and EWGDRS motifs characteristic of UPF0016 transporters. These findings establish Gdt1 as a key determinant of Ca²⁺ and Mn²⁺ regulation and support a complementary role for Gdt2 in ion regulation, a process essential for efficient glycosylation and normal cell wall morphogenesis.