title: Sequence-specific, nanomolar peptide binding via cucurbit[8]uril-induced folding and inclusion of neighboring side chains.
abstract: This paper describes the molecular recognition of the tripeptide Tyr-Leu-Ala by the synthetic receptor cucurbit[8]uril (Q8) in aqueous buffer with nanomolar affinity and exceptional specificity. This combination of characteristics, which also applies to antibodies, is desirable for applications in biochemistry and biotechnology but has eluded supramolecular chemists for decades. Building on prior knowledge that Q8 binds to peptides with N-terminal aromatic residues, a library screen of 105 peptides was designed to test the effects of residues adjacent to N-terminal Trp, Phe, or Tyr. The screen used tetramethylbenzobis(imidazolium) (MBBI) as a fluorescent indicator and resulted in the unexpected discovery that MBBI can serve not only as a turn-off sensor via the simultaneous inclusion of a Trp residue but also as a turn-on sensor via the competitive displacement of MBBI upon binding of Phe- or Tyr-terminated peptides. The unusual fluorescence response of the Tyr series prompted further investigation by (1)H NMR spectroscopy, electrospray ionization mass spectrometry, and isothermal titration calorimetry. From these studies, a novel binding motif was discovered in which only 1 equiv of peptide binds to Q8, and the side chains of both the N-terminal Tyr residue and its immediate neighbor bind within the Q8 cavity. For the peptide Tyr-Leu-Ala, the equilibrium dissociation constant value is 7.2 nM, whereas that of its sequence isomer Tyr-Ala-Leu is 34 μM. The high stability, recyclability, and low cost of Q8 combined with the straightforward incorporation of Tyr-Leu-Ala into recombinant proteins should make this system attractive for the development of biological applications.
authors.affiliation: Department of Chemistry, Trinity University, San Antonio, Texas 78212, United States.
authors.forename: Lauren C
authors.initials: LC
authors.lastname: Smith
authors.affiliation: Department of Chemistry, Trinity University, San Antonio, Texas 78212, United States.
authors.forename: David G
authors.initials: DG
authors.lastname: Leach
authors.affiliation: Department of Chemistry, Trinity University, San Antonio, Texas 78212, United States.
authors.forename: Brittney E
authors.initials: BE
authors.lastname: Blaylock
authors.affiliation: Department of Chemistry, Trinity University, San Antonio, Texas 78212, United States.
authors.forename: Omar A
authors.initials: OA
authors.lastname: Ali
authors.affiliation: Department of Chemistry, Trinity University, San Antonio, Texas 78212, United States.
authors.forename: Adam R
authors.initials: AR
authors.lastname: Urbach
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry*; D019151:Peptide Library; D010649:Phenylalanine; D017510:Protein Folding; D013816:Thermodynamics; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D007093:Imidazoles; D009842:Oligopeptides; D019151:Peptide Library; D010649:Phenylalanine; C507198:cucurbit(8)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils; C000605450:tyrosyl-leucyl-alanine