title: Host-guest chemistry in the gas phase: selected fragmentations of CB[6]-peptide complexes at lysine residues and its utility to probe the structures of small proteins.
abstract: The gas phase host-guest chemistry between cucurbit[6]uril (CB[6]) and peptide is investigated using electrospray ionization mass spectrometry (ESI-MS). CB[6] exhibits a high preference to interacting with a Lys residue in a peptide forming a CB[6]-peptide complex. Collisionally activated CB[6] complexes of peptides yield a common highly selective fragment product at m/z 549.2, corresponding to the doubly charged CB[6] complex of 5-iminiopentylammonium (5IPA). The process involves the formation of an internal iminium ion, which results from further fragments to an a-type ion from a y-type ion, and the resulting 5IPA ion threads through CB[6]. Numerous peptides are investigated to test the generality of the observed unique host-guest chemistry of CB[6]. Its potential utility in probing protein structures is demonstrated using CB[6] complexes of ubiquitin. Low-energy collision induced dissociation yields CB[6] complex fragments, and further MS(n) spectra reveal details of the CB[6] binding sites, which allow us to deduce the protein structure in the solution phase. The mechanisms and energetics of the observed reactions are evaluated using density functional theory calculations.
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, 790-784, Republic of Korea.
authors.forename: Sung Woo
authors.initials: SW
authors.lastname: Heo
authors.forename: Tae Su
authors.initials: TS
authors.lastname: Choi
authors.forename: Kyung Man
authors.initials: KM
authors.lastname: Park
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Ko
authors.forename: Seung Bin
authors.initials: SB
authors.lastname: Kim
authors.forename: Kimoon
authors.initials: K
authors.lastname: Kim
authors.forename: Hugh I
authors.initials: HI
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D001952:Bridged-Ring Compounds / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D008239:Lysine / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D025801:Ubiquitin / Q000737:chemistry; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D005740:Gases; D007093:Imidazoles; D008239:Lysine; D010455:Peptides; D025801:Ubiquitin; C454805:cucurbit(6)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils