Abstract: The invention concerns novel streptavidin muteins. In one embodiment such a the mutein (a) contains at least two cysteine residues in the region of the amino acid positions 44 to 53 with reference to the amino acid sequence of wild type streptavidin as set forth at SEQ ID NO: 212 and (b) has a higher binding affinity than (i) a streptavidin mutein “1” (SEQ ID NO: 112) that comprises the amino acid sequence Val44-Thr45-Ala46-Arg47 (SEQ ID NO: 98), or (ii) wild type-streptavidin of which amino acid residues 14 to 139 are shown as SEQ ID NO: 212 for peptide ligands comprising the amino acid sequence Trp-Ser-His-Pro-Gln-Phe-Glu-Lys (SEQ ID NO: 100).

Abstract: The invention concerns novel streptavidin muteins and methods of determining, immobilizing, isolating or purifying proteins under denaturing conditions. In one embodiment such a mutein has an Cys residue at sequence position 127 of the wild-type sequence of streptavidin and comprises at least one mutation in the region of the amino acid positions 117 to 121 with reference to the amino acid sequence of wild type streptavidin.

Abstract: The invention concerns novel streptavidin muteins and their use for determination, isolation or purification of proteins under denaturing conditions. In one embodiment such a mutein has an Cys residue at sequence position 127 of the wild-type sequence of streptavidin and comprises at least one mutation in the region of the amino acid positions 115 to 121 with reference to the amino acid sequence of wild type streptavidin.

Abstract: The invention provides new methods of isolating target cells using a solid phase, the solid phase comprising a ligand L wherein the ligand L is capable of specifically binding a ligand binding partner LB, the ligand binding partner LB being present in a receptor molecule binding reagent or a multimerization reagent used for isolating target cells. The invention also provides corresponding new arrangements and devices for isolating a target cell from a sample.