title: Pulse EPR-enabled interpretation of scarce pseudocontact shifts induced by lanthanide binding tags.
abstract: Pseudocontact shifts (PCS) induced by tags loaded with paramagnetic lanthanide ions provide powerful long-range structure information, provided the location of the metal ion relative to the target protein is known. Usually, the metal position is determined by fitting the magnetic susceptibility anisotropy (Δχ) tensor to the 3D structure of the protein in an 8-parameter fit, which requires a large set of PCSs to be reliable. In an alternative approach, we used multiple Gd(3+)-Gd(3+) distances measured by double electron-electron resonance (DEER) experiments to define the metal position, allowing Δχ-tensor determinations from more robust 5-parameter fits that can be performed with a relatively sparse set of PCSs. Using this approach with the 32 kDa E. coli aspartate/glutamate binding protein (DEBP), we demonstrate a structural transition between substrate-bound and substrate-free DEBP, supported by PCSs generated by C3-Tm(3+) and C3-Tb(3+) tags attached to a genetically encoded p-azidophenylalanine residue. The significance of small PCSs was magnified by considering the difference between the chemical shifts measured with Tb(3+) and Tm(3+) rather than involving a diamagnetic reference. The integrative sparse data approach developed in this work makes poorly soluble proteins of limited stability amenable to structural studies in solution, without having to rely on cysteine mutations for tag attachment.
authors.affiliation: Research School of Chemistry, Australian National University, Canberra, ACT, 2601, Australia.
authors.forename: Elwy H
authors.initials: EH
authors.lastname: Abdelkader
authors.affiliation: Research School of Chemistry, Australian National University, Canberra, ACT, 2601, Australia.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Yao
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science, 76100, Rehovot, Israel.
authors.forename: Akiva
authors.initials: A
authors.lastname: Feintuch
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.
authors.forename: Luke A
authors.initials: LA
authors.lastname: Adams
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.
authors.forename: Luigi
authors.initials: L
authors.lastname: Aurelio
authors.affiliation: Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia.
authors.forename: Bim
authors.initials: B
authors.lastname: Graham
authors.affiliation: Department of Chemical Physics, Weizmann Institute of Science, 76100, Rehovot, Israel.
authors.forename: Daniella
authors.initials: D
authors.lastname: Goldfarb
authors.affiliation: Research School of Chemistry, Australian National University, Canberra, ACT, 2601, Australia. gottfried.otting@anu.edu.au.
authors.forename: Gottfried
authors.initials: G
authors.lastname: Otting
mesh_terms: D000465:Algorithms; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: D011506:Proteins
keywords: Double electron–electron resonance; E. coli aspartate/glutamate binding protein; Integrative structural biology; Lanthanide tag; Pseudocontact shift