title: Structural characterization of an unusually stable cyclic peptide, kalata B2 from Oldenlandia affinis.
abstract: Kalata peptides are isolated from an African medicinal plant, Oldenlandia affinis, an aqueous decoction of which can be ingested to accelerate uterine contraction during childbirth. The closely packed disulfide core of kalata peptides confers unusual stability against thermal, chemical, and enzymatic degradation. The molecular arrangement may hamper NMR-assisted disulfide connectivity assignment. We have combined NMR with high-resolution mass spectrometry (MS) and MS/MS of native and chemically derivatized kalata B2 to determine its amino acid sequence and disulfide connectivity. Infrared multiphoton dissociation establishes the disulfide bond linkages in kalata B2 as I-IV, II-V and III-VI.
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
authors.forename: Sudarslal Sadasivan
authors.initials: SS
authors.lastname: Nair
authors.forename: Julija
authors.initials: J
authors.lastname: Romanuka
authors.forename: Martin
authors.initials: M
authors.lastname: Billeter
authors.forename: Lars
authors.initials: L
authors.lastname: Skjeldal
authors.forename: Mark R
authors.initials: MR
authors.lastname: Emmett
authors.forename: Carol L
authors.initials: CL
authors.lastname: Nilsson
authors.forename: Alan G
authors.initials: AG
authors.lastname: Marshall
mesh_terms: D000595:Amino Acid Sequence; D047169:Cyclotides / Q000737:chemistry / Q000302:isolation & purification; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D032067:Oldenlandia / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation
chemical_list: D047169:Cyclotides; D010456:Peptides, Cyclic; C561323:kalata B2