YeeD is an essential partner for YeeE-mediated thiosulfate uptake in bacteria and regulates thiosulfate ion decomposition.

Uptake of thiosulfate ions as an inorganic sulfur source from the environment is important for bacterial sulfur assimilation. Recently, a selective thiosulfate uptake pathway involving a membrane protein YeeE (TsuA) in Escherichia coli was characterized. YeeE-like proteins are conserved in some bacteria, archaea, and eukaryotes. However, the precise function of YeeE, along with its potential partner protein in the thiosulfate ion uptake pathway, remained unclear. Here, we assessed selective thiosulfate transport via Spirochaeta thermophila YeeE in vitro and characterized E. coli YeeD (TsuB) as an adjacent and essential protein for YeeE-mediated thiosulfate uptake in vivo. We further showed that S. thermophila YeeD possesses thiosulfate decomposition activity and that a conserved cysteine in YeeD was modified to several forms in the presence of thiosulfate. Finally, the crystal structures of S. thermophila YeeE-YeeD fusion proteins at 3.34-Å and 2.60-Å resolutions revealed their interactions. The association was evaluated by a binding assay using purified S. thermophila YeeE and YeeD. Based on these results, a model of the sophisticated uptake of thiosulfate ions by YeeE and YeeD is proposed.

Silica adsorption tag derived from the silica polycondensation protein glassin for the immobilization of soluble proteins.

Glassin is a water-soluble protein from the siliceous skeleton of a marine sponge that adsorbs tightly to silica at pH 7.0-9.0 and accelerates silica particle formation from silicic acid. Glassin comprises three distinct domains: a His and Asp-rich (HD) domain, a Pro-rich (P) domain, and a His and Thr-rich (HT) domain. Here, we investigated the roles of these three domains in silica adsorption by using glutathione S-transferase (GST) fused with glassin or with each domain. GST fused with the HD domain exhibited tight adsorption, equivalent to that of GST fused with the full-length glassin sequence at values above 7.0. The apparent Kd values for the binding of full-length glassin and HD to fumed silica at pH 7.0 were 20.8 and 22.7 nM, respectively, indicating that this domain greatly contributes to the silica adsorption ability of glassin. In addition, no internal cleavage was observed in the HD domain, whereas GST fused with the full-length glassin sequence exhibited internal cleavage. The HD domain adsorbed on silica did not dissociate even at pH 6.0. Given these findings, we concluded that the HD domain has potential as a tag for the immobilization of soluble proteins.