Publications
bioRxiv : the preprint server for biologySep 2025 DOI:
10.1101/2025.08.29.672704

Optimal TELSAM-Target Protein Linker Character is Target Protein-Dependent

Romo, Maria Jose Pedroza; Keliiliki, Alihikaua; Averett, Jacob C; Gonzalez, Joseph F; Noakes, Ethan; Wilson, Elijah W; Smith, Conrad; Averett, Blake; Hansen, Dalton; Nickles, Riley; Bradford, Miles; Soleimani, Sara; Smith, Tobin; Nawarathnage, Supeshala; Samarwickrama, Prasadika; Kelsch, Ariel; Bunn, Derick; Stewart, Cameron; Abiodun, Wisdom; Tsubaki, Evan; Brown, Seth; Doukov, Tzanko I; Moody, James D
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Abstract
Fusing a variant of the sterile alpha motif domain of the human translocation ETS leukaemia protein (TELSAM) to a protein of interest has been shown to significantly enhance crystallization propensity. TELSAM is a pH-dependent, polymer-forming protein crystallization chaperone which, when covalently fused to a protein of interest, forms a stable, well-ordered crystal lattice. However, despite its success, a challenge persists in that crystal quality and diffraction limits appear to be heavily dependent on the choice of linker between TELSAM and the protein of interest, with identification of a functional linker relying on trial-and-error methods. Likewise, previous studies revealed that the 10xHis tag at the TELSAM N-terminus can either facilitate or hinder the ordered crystallization of target proteins attached via flexible or semi-flexible linkers. To address these challenges, we designed multiple constructs with several types of linkers-rigid (helical fusion), semi-flexible (Pro-Alan), and flexible (poly-Gly)-of varying lengths to fuse a designed ankyrin repeat protein (DARPin) to the TELSAM C-terminus. Semi-flexible and flexible linker constructs were made with and without the 10xHis tag. Our findings indicate that short semi-flexible and rigid linkers consistently yield large crystals within 24 hours with a DARPin target protein, but that flexible linkers perform best with a TNK1 UBA domain target protein. Removing the 10xHis tag enhanced crystallization rates, improved crystal morphology, and increased the crystallization propensity of semi-flexible and flexible linker constructs. While removing the His tag did not have a significant effect on crystal size, it improved the diffraction limits and crystal quality of the 1TEL-PA-DARPin construct. These results suggest that the ideal linker selection primarily depends on the properties of the target protein. Our data support the recommendation to use a short yet flexible or semi-flexible linker between TELSAM and the target protein to facilitate protein crystallization and high-resolution structure determination.
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