Updated project metadata. Lanthanides were recently discovered as metals required in the active site of certain methanol dehydrogenases. Since then, the characterization of the lanthanome, i.e. all 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 Methylobacillus 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 presence of lanthanum (Xox proteins, TonB-dependent receptor), we also identified several novel proteins not previously associated with lanthanide utilization. Among these was Mfla_0908, a periplasmic 19 kDa-protein without functional annotation. The protein comprises two characteristic PepSY domains and we thus termed the protein lanpepsy (LanP). Based on bioinformatic analysis, we speculated that LanP could be involved in lanthanide binding. Using dye competition assays as well as protein ultrafiltration followed by inductively coupled plasma mass spectrometric analysis, we demonstrated the presence of four lanthanide binding sites that showed selectivity over the chemically similar Ca2+ ion. A similar arrangement of two PepSY domains is also present in the recently described uranium-binding protein UipA from Microbacterium spp. LanP and UipA thus represent the first members of PepSY domain proteins involved in metal binding. Although the physiological role of LanP is still unclear, its discovery has important implications for applications towards the sustainable purification and separation of lanthanides.