レアアースを分離する細菌タンパク質を発見(Bacterial protein discovered, engineered to better separate rare earth metals)

2024-10-29 ペンシルベニア州立大学(PennState)

<関連情報>

• https://www.psu.edu/news/research/story/bacterial-protein-discovered-engineered-better-separate-rare-earth-metals
• https://www.pnas.org/doi/10.1073/pnas.2410926121
• https://medibio.tiisys.com/111761/

ランタニド・シャペロンタンパク質の金属中心二量体化を調節して軽ランタニドの分離を実現 Modulating metal-centered dimerization of a lanthanide chaperone protein for separation of light lanthanides

Wyatt B. Larrinaga, Jonathan J. Jung, Chi-Yun Lin, +1, and Joseph A. Cotruvo Jr.
Proceedings of the National Academy of Sciences  Published:October 28, 2024
DOI:https://doi.org/10.1073/pnas.2410926121

Significance

Ligand design to effectively discriminate between, and thereby separate, adjacent lanthanide(III) ions is a long-standing challenge. In this work, biochemical studies and X-ray structures reveal how a protein involved in lanthanide uptake binds lanthanide ions, and they suggest that it may help ensure the selective cytosolic import of only the largest lanthanides by siphoning off other lanthanides in the periplasm of lanthanide-utilizing bacteria. Engineering this protein’s molecular interface yields separation factors among light lanthanides (lanthanum, cerium, praseodymium, and neodymium) that are comparable to industrial extractants, demonstrating the utility of metal-centered protein dimerization to facilitate difficult separations under mild, aqueous conditions.

Abstract

Elucidating details of biology’s selective uptake and trafficking of rare earth elements, particularly the lanthanides, has the potential to inspire sustainable biomolecular separations of these essential metals for myriad modern technologies. Here, we biochemically and structurally characterize Methylobacterium (Methylorubrum) extorquens LanD, a periplasmic protein from a bacterial gene cluster for lanthanide uptake. This protein provides only four ligands at its surface-exposed lanthanide-binding site, allowing for metal-centered protein dimerization that favors the largest lanthanide, La^III. However, the monomer prefers Nd^III and Sm^III, which are disfavored lanthanides for cellular utilization. Structure-guided mutagenesis of a metal-ligand and an outer-sphere residue weakens metal binding to the LanD monomer and enhances dimerization for Pr^III and Nd^III by 100-fold. Selective dimerization enriches high-value Pr^III and Nd^III relative to low-value La^III and Ce^III in an all-aqueous process, achieving higher separation factors than lanmodulins and comparable or better separation factors than common industrial extractants. Finally, we show that LanD interacts with lanmodulin (LanM), a previously characterized periplasmic protein that shares LanD’s preference for Nd^III and Sm^III. Our results suggest that LanD’s unusual metal-binding site transfers less-desirable lanthanides to LanM to siphon them away from the pathway for cytosolic import. The properties of LanD show how relatively weak chelators can achieve high selectivity, and they form the basis for the design of protein dimers for separation of adjacent lanthanide pairs and other metal ions.