2y3f
Traptavidin, biotin bound form
Structural highlights
FunctionSAV_STRAV The biological function of streptavidin is not known. Forms a strong non-covalent specific complex with biotin (one molecule of biotin per subunit of streptavidin). Publication Abstract from PubMedThe interaction between streptavidin and biotin is one of the strongest non-covalent interactions in nature. Streptavidin is a widely used tool and a paradigm for protein-ligand interactions. We recently developed a streptavidin mutant, termed traptavidin, possessing 10-fold lower off-rate for biotin, with increased mechanical and thermal stability. Here, we determined crystal structures of apo-traptavidin and biotin-traptavidin at 1.5 A resolution. In apo-streptavidin the L3/4 loop, near biotin's valeryl tail, is typically disordered and open, but closes upon biotin binding. In contrast, this L3/4 loop was shut in both apo-traptavidin and biotin-traptavidin. The reduced flexibility of L3/4 and decreased conformational change on biotin binding provide an explanation for traptavidin's reduced biotin off-rate and on-rate. The L3/4 loop includes Ser-45, which forms a hydrogen bond to biotin consistently in traptavidin but erratically in streptavidin. Reduced breakage of the biotin:Ser-45 hydrogen bond in traptavidin is likely to inhibit the initiating event in biotin's dissociation pathway. We generated a traptavidin with 1 biotin binding site rather than 4, which showed a similarly slow off-rate, demonstrating that traptavidin's slow off-rate was governed by intra-subunit effects. Understanding the structural features of this tenacious interaction may assist design of even stronger affinity tags and inhibitors. How the biotin-streptavidin interaction was made even stronger: investigation via crystallography and a chimeric tetramer.,Chivers CE, Koner AL, Lowe ED, Howarth M Biochem J. 2011 Jan 18. PMID:21241253[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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