9E7J

Cu-bound tetrameric copper storage protein 1 with anti-rhodopsin 1D4 epitope

Summary for 9E7J

• Entry DOI: 10.2210/pdb9e7j/pdb
• EMDB information: 47678
• Descriptor: Four-helix bundle copper-binding protein (1 entity in total)
• Functional Keywords: tetrameric copper storage protein 1, metal binding protein
• Biological source: Methylosinus trichosporium OB3b
• Total number of polymer chains: 4
• Total formula weight: 45284.54

Authors

Yao, Y.,Oken, A.C.,Farrens, D.L. (deposition date: 2024-11-01, release date: 2025-05-07, Last modification date: 2025-07-23)

Primary citation

Yao, W.,Oken, A.C.,Farrens, D.L.
A novel "bio-tag" for cryo-EM studies based on the small, electron-dense protein Csp1.
Biophys.J., 124:1414-1423, 2025

PubMed Abstract: Small proteins can be challenging to study by single-particle cryogenic electron microscopy (cryo-EM) techniques because they have low signal-to-noise ratios, making them difficult to identify and analyze. Here we investigated the use of Csp1, a small (∼50 kDa) tetrameric metal-binding protein, to act as a "bio-tag" to help overcome this problem. We find Csp1 is compact, stable, and exhibits enhanced electron scattering and excellent particle contrast in cryo-EM micrographs. As a result, we could determine the structure of Csp1 to 2.98-Å resolution using standard cryo-EM approaches. We also tested if Csp1 could be used as a tag or fiducial to help determine the structure of a protein bound to it. Specifically, we analyzed an epitope-tagged Csp1 bound to a ∼40 kDa Fab fragment from the antibody 1D4. Data from these complexes yielded medium-resolution structures of the complex (5.70 Å) and the bound 1D4 Fab (5.40 Å). These results suggest that, with further optimization, electron-rich Csp1 is a promising bio-tag for use in cryo-EM studies.

PubMed: 40620219
DOI: 10.1016/j.bpj.2025.03.018

Experimental method

ELECTRON MICROSCOPY (2.98 Å)