title: Picosecond fluorescence spectroscopy of a single-chain class I major histocompatibility complex encoded protein in its peptide loaded and unloaded states.
abstract: The tryptophan fluorescence properties of two different peptide complexes of the single-chain H-2Kd (SC-Kd) were studied by means of the single-photon counting technique. The latter enables time-resolved measurements of fluorescence intensity and anisotropy decay parameters relevant to structural and dynamic properties of proteins. While the isolated SC-Kd molecules in their 'original' purified form represent the unloaded state, i.e., containing endogenous low-affinity peptides, the loaded SC-Kd protein is obtained by introducing well-defined high-affinity peptides that replace the low-affinity ones. These two SC-Kd forms were found to exhibit different time-resolved tryptophan emission patterns; the unloaded complexes show a slightly faster fluorescence intensity decay rate than the loaded one. Three well-resolved time domains were distinguished in the anisotropy decay course of both forms: a short one in the picosecond range, an intermediate one of several nanoseconds, and a long one spanning several dozens to hundreds of nanoseconds. They are assigned to superposition contributions of (short- and long-distance) non-radiative energy transfer processes, to motions of the tryptophans, and to rotation of the whole protein globule. In the loaded SC-Kds, the first two processes were found to be attenuated. It is therefore suggested that upon binding of high-affinity peptides, the SC-Kd structure becomes more compact and certain tryptophans become less accessible to quenchers. The faster anisotropy decay observed in the unloaded form reflects both an enhancement in the energy-transfer between the tryptophans and an acceleration of their motions.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: K
authors.initials: K
authors.lastname: Dittes
authors.forename: D M
authors.initials: DM
authors.lastname: Gakamsky
authors.forename: G
authors.initials: G
authors.lastname: Haran
authors.forename: E
authors.initials: E
authors.lastname: Haas
authors.forename: D M
authors.initials: DM
authors.lastname: Ojcius
authors.forename: P
authors.initials: P
authors.lastname: Kourilsky
authors.forename: I
authors.initials: I
authors.lastname: Pecht
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005454:Fluorescence Polarization; D006183:H-2 Antigens / Q000737:chemistry*; D009980:Influenza A virus; D051379:Mice; D008969:Molecular Sequence Data; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry; D010962:Plasmodium berghei; D015800:Protozoan Proteins / Q000737:chemistry*; D016601:RNA-Binding Proteins; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000032:analysis; D014758:Viral Core Proteins / Q000737:chemistry*
chemical_list: D006183:H-2 Antigens; C024755:H-2K(K) antigen; C048842:NP protein, Influenza A virus; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins; D009842:Oligopeptides; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; D014758:Viral Core Proteins; D014364:Tryptophan