1. Immunization with plasmid DNA encoding MHC class II binding peptide/CLIP-replaced invariant chain (Ii) induces specific helper T cells in vivo: the assessment of Ii p31 and p41 isoforms as vehicles for immunization
T Nagata, T Higashi, T Aoshi, M Suzuki, M Uchijima, Y Koide Vaccine. 2001 Oct 12;20(1-2):105-14. doi: 10.1016/s0264-410x(01)00310-3.
A single helper T cell (Th) epitope-specific T cell subset was successfully induced in vivo by immunization with plasmid DNA encoding MHC class II binding peptide/class II-associated invariant chain peptide (CLIP)-replaced murine Ii molecules. Spleen cells from mice immunized by gene gun bombardment with plasmid DNA for Ii p31 and p41 molecules, whose CLIP regions were replaced with an I-A(d)-restricted Th epitope, ovalbumin (OVA) 323-336, showed the specific proliferation and interferon-gamma (IFN-gamma) production. A20-2J B cell lines having these plasmids were capable of stimulating spleen cells from the immunized mice and naïve DO10-transgenic mice bearing the epitope-specific T cell receptor (TCR) transgenes by examining the specific proliferative response and IFN-gamma production. Some mice immunized with the Ii p41-OVA323, but not with the Ii p31-OVA323 plasmid, produced the peptide-specific antibodies, suggesting the functional difference between Ii isoforms.
2. Effect of conformational propensity of peptide antigens in their interaction with MHC class II molecules. Failure to document the importance of regular secondary structures
A Sette, A Lamont, S Buus, S M Colon, C Miles, H M Grey J Immunol. 1989 Aug 15;143(4):1268-73.
In an attempt to define some of the conformational requirements for binding of the antigenic peptide OVA 323-336 to purified IAd molecules, three distinct experimental approaches were applied. First, the effect of introducing proline or glycine residues within the region of OVA 323-336 crucial for its IAd binding capacity was analyzed. In most instances these substitutions had little or no effect, suggesting that neither alpha-helical nor beta-sheet regular structures may be strictly required for productive interaction with MHC molecules. Some of the same substitutions were also found to have no effect on the capacity of the peptide to stimulate OVA 323-336 specific T cell hybridomas, suggesting that regular structures such as alpha-helices or beta-sheets may not be strictly required for T cell stimulation, either. Second, we introduced, within the OVA 323-336 molecule, structural modifications predicted to alter its dipole characteristics and stabilize helical structures. No improvement of the IAd binding capacity was detected following these structural alterations. Surprisingly, some but not others of these analogs displayed increased antigenicity for OVA 323-336 specific T cell hybridomas. Third, a panel of analogs of OVA 323-336 were synthesized in which the crucial IAd binding core region was linked to non-native sequences of differing conformational propensities. When 22 such analogs were tested for IAd binding, it was found that these non-native sequences could drastically influence the binding capacity, but no correlation was found between their effect and their alpha-helical, beta-sheet, or beta-turn conformational propensity as calculated by the Chou and Fasman algorithm. In summary, all the data presented herein suggest that, at least in the case of OVA 323-336 and IAd, the propensity of the antigen molecule to form secondary structures such as alpha-helices, beta-sheets, or beta-turns does not correlate with its capacity to bind MHC molecules.
3. Purification and properties of the Escherichia coli nucleoside transporter NupG, a paradigm for a major facilitator transporter sub-family
Hao Xie, et al. Mol Membr Biol. 2004 Sep-Oct;21(5):323-36. doi: 10.1080/09687860400003941.
NupG from Escherichia coli is the archetype of a family of nucleoside transporters found in several eubacterial groups and has distant homologues in eukaryotes, including man. To facilitate investigation of its molecular mechanism, we developed methods for expressing an oligohistidine-tagged form of NupG both at high levels (>20% of the inner membrane protein) in E. coli and in Xenopus laevis oocytes. In E. coli recombinant NupG transported purine (adenosine) and pyrimidine (uridine) nucleosides with apparent K(m) values of approximately 20-30 microM and transport was energized primarily by the membrane potential component of the proton motive force. Competition experiments in E. coli and measurements of uptake in oocytes confirmed that NupG was a broad-specificity transporter of purine and pyrimidine nucleosides. Importantly, using high-level expression in E. coli and magic-angle spinning cross-polarization solid-state nuclear magnetic resonance, we have for the first time been able directly to measure the binding of the permeant ([1'-(13)C]uridine) to the protein and to assess its relative mobility within the binding site, under non-energized conditions. Purification of over-expressed NupG to near homogeneity by metal chelate affinity chromatography, with retention of transport function in reconstitution assays, was also achieved. Fourier transform infrared and circular dichroism spectroscopy provided further evidence that the purified protein retained its 3D conformation and was predominantly alpha-helical in nature, consistent with a proposed structure containing 12 transmembrane helices. These findings open the way to elucidating the molecular mechanism of transport in this key family of membrane transporters.
