Lanpepsy is a novel lanthanide-binding protein involved in the lanthanide response of the obligate methylotroph Methylobacillus flagellatus

Lanthanides were recently discovered as metals required in the active site of certain methanol dehydrogenases. Since then, the characterization of the lanthanome, that is, proteins involved in sensing, uptake, and utilization of lanthanides, has become an active field of research. Initial exploration of the response to lanthanides in methylotrophs has revealed that the lanthanome is not conserved and that multiple mechanisms for lanthanide utilization must exist. Here, we investigated the lanthanome in the obligate model methylotroph Methyl-obacillus flagellatus. We used a proteomic approach to analyze differentially regulated proteins in the presence of lanthanum. While multiple known proteins showed induction upon growth in the presence of lanthanum (Xox proteins, TonB-dependent receptor), we also identified several novel proteins not previ-ously associated with lanthanide utilization. Among these was Mfla_0908, a periplasmic 19 kDa protein without functional annotation. The protein comprises two characteristic PepSY domains, which is why we termed the protein lanpepsy (LanP). Based on bioinformatic analysis, we speculated that LanP could be involved in lanthanide binding. Using dye competition as-says, quantification of protein-bound lanthanides by induc-tively coupled plasma mass spectrometry, as well as isothermal titration calorimetry, we demonstrated the presence of multi-ple lanthanide binding sites that showed selectivity over the chemically similar calcium ion. LanP thus represents the first member of the PepSY family that binds lanthanides. Although the physiological role of LanP is still unclear, its identification is of interest for applications toward the sustainable purifica-tion and separation of rare-earth elements.

Automated summary

Lanthanides are required in certain methanol dehydrogenases, and the study of proteins involved in lanthanide sensing and utilization has become a popular field of research. This study focused on the lanthanome of Methyl-obacillus flagellatus and identified a novel lanthanide-binding protein called LanP. Bioinformatic analysis and experimental assays confirmed the presence of multiple lanthanide binding sites in LanP, highlighting its potential role in lanthanide utilization. This discovery has implications for the purification and separation of rare-earth elements.