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Publication Abstract from PubMed

The affinity system based on the artificial peptide ligand Strep-tag(R) II and engineered tetrameric streptavidin, known as Strep-Tactin(R), offers attractive applications for the study of recombinant proteins, from detection and purification to functional immobilization. To further improve binding of the Strep-tag II to streptavidin we have subjected two protruding loops that shape its ligand pocket for the peptide - instead of D-biotin recognized by the natural protein - to iterative random mutagenesis. Sequence analyses of hits from functional screening assays revealed several unexpected structural motifs, such as a disulfide bridge at the base of one loop, replacement of the crucial residue Trp120 by Gly and a two-residue deletion in the second loop. The mutant m1-9 (dubbed Strep-Tactin XT) showed strongly enhanced affinity towards the Strep-tag II, which was further boosted in case of the bivalent Twin-Strep-tag(R). Four representative streptavidin mutants were crystallized in complex with the Strep-tag II peptide and their X-ray structures were solved at high resolutions. In addition, the crystal structure of the complex between Strep-Tactin XT and the Twin-Strep-tag was elucidated, indicating a bivalent mode of binding and explaining the experimentally observed avidity effect. Our study illustrates the structural plasticity of streptavidin as a scaffold for ligand binding and reveals interaction modes that would have been difficult to predict. As result, Strep-Tactin XT offers a convenient reagent for the kinetically stable immobilization of recombinant proteins fused with the Twin-Strep-tag. The possibility of reversibly dissociating such complexes simply with D-biotin as a competing ligand enables functional studies in protein science as well as cell biology.

The Role of Changing Loop Conformations in Streptavidin Versions Engineered for High-affinity Binding of the Strep-tag II Peptide.,Schmidt TGM, Eichinger A, Schneider M, Bonet L, Carl U, Karthaus D, Theobald I, Skerra A J Mol Biol. 2021 Apr 30;433(9):166893. doi: 10.1016/j.jmb.2021.166893. Epub 2021 , Feb 24. PMID:33639211^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.