Selective detection of mobile amino acid resonances of chloroplast ATP synthase by proton spin-echo NMR

High mobility of N-terminal parts of A and B subunits of ricin

1H-NMR spectra (500 MHz) of ricin and its isolated A and B subunits have been analyzed in this study. It is shown that together with tight packing of the polypeptide chain there also exist flexible highly mobile segments in the structure of the proteins. Examination of the line-widths of resonances and the identification of sharp signals with protons of amino acids indicates that N-terminal peptide segments of A and B subunits are free and undergo rapid segmental motions. Spin-echo sequence (90-tau-180-tau) was used to suppress an intensive unresolved background signal from protons involved in the globular part of ricin, thus permitting selective identification of the unusually sharp signals from mobile side chains.

Biochemical and proton NMR characterization of the isolated functional beta-subunit of coupling factor one from spinach chloroplasts

Beta subunits have been dissociated from CF1 of spinach chloroplasts, purified by HPLC and characterized by two-dimensional electrophoresis and fluorescence emission. The solutions of isolated beta subunits are able to hydrolyze MgATP; this ATPase activity is an intrinsic property of the beta molecule. From proton NMR at 300 and 500 MHz, it is shown that the preparations are fully reproducible and that beta subunits remain monomeric with 75% aliphatic protons associated with rigid parts of the molecule. The other 25% give rise to separate resonances and belong to mobile side-chains and/or to flexible regions. The measurement of the transverse relaxation times T2 has permitted a detailed characterization of the molecular dynamics of the isolated beta subunits.