9CLC

Crystal structure of maltose binding protein (Apo), mutant Trp10 to 4-Cyanotryptophan

This is a non-PDB format compatible entry.

Summary for 9CLC

• Entry DOI: 10.2210/pdb9clc/pdb
• Descriptor: Maltose/maltodextrin-binding periplasmic protein, SODIUM ION, CADMIUM ION, ... (7 entities in total)
• Functional Keywords: solute binding protein, non-canonical amino acid incorporation, sugar binding protein
• Biological source: Escherichia coli
• Total number of polymer chains: 1
• Total formula weight: 42807.11

Authors

Habel, E.,Frkic, R.L.,Jackson, C.J.,Huber, T.,Otting, G. (deposition date: 2024-07-10, release date: 2024-12-18, Last modification date: 2025-03-19)

Primary citation

Qianzhu, H.,Abdelkader, E.H.,Welegedara, A.P.,Habel, E.,Paul, N.,Frkic, R.L.,Jackson, C.J.,Huber, T.,Otting, G.
Rendering Proteins Fluorescent Inconspicuously: Genetically Encoded 4-Cyanotryptophan Conserves Their Structure and Enables the Detection of Ligand Binding Sites.
Angew.Chem.Int.Ed.Engl., 64:e202421000-e202421000, 2025

PubMed Abstract: Cyanotryptophans (CN-Trp) are privileged multimodal reporters on protein structure. They are similar in size to the canonical amino acid tryptophan and some of them exhibit bright fluorescence which responds sensitively to changes in the environment. We selected aminoacyl-tRNA synthetases specific for 4-, 5-, 6-, and 7-CN-Trp for high-yield in vivo production of proteins with a single, site-specifically introduced nitrile label. The absorption maximum of 4-CN-Trp is distinct from Trp, allowing the selective excitation of its intense fluorescence. 4-CN-Trp fluoresces in the visible range with an intensity rivalling that of 7-hydroxy-coumarin. Crystal structures of maltose binding protein demonstrate near-complete structural conservation when a native buried Trp residue is replaced by 4-CN-Trp. Besides presenting an inconspicuous tag for live cell microscopy, the intense fluorescence of 4-CN-Trp enables measurements of subnanomolar ligand binding affinities in isotropic solution, as demonstrated by the complex between rapamycin and the peptidyl-prolyl isomerase FKBP12 furnished with a 4-CN-Trp residue in the substrate binding pocket. Furthermore, 4-CN-Trp residues positioned at different locations of a protein containing multiple tryptophan residues permits using fluorescence quenching experiments to detect the proximity of individual Trp residues to the binding site of aromatic ligands.

PubMed: 39632265
DOI: 10.1002/anie.202421000

Experimental method

X-RAY DIFFRACTION (1.48 Å)