title: Localization of 13 one-helix integral membrane proteins in photosystem II subcomplexes.
abstract: Photosystem II is a multimeric protein complex of the thylakoid membrane in chloroplasts. Approximately half of the at least 26 different integral membrane protein subunits have molecular masses lower than 10 kDa. After one-dimensional (1D) or two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE) separation, followed by enzymatic digestion of detected proteins, hardly any of these low-molecular-weight (LMW) subunits are detectable. Therefore, we developed a method for the analysis of highly hydrophobic LMW proteins. Intact proteins are extracted from acrylamide gels using a mixture of formic acid and organic solvent, precipitated with acetone, and analyzed by "top-down" mass spectrometry (MS). After offline nanoESI (electrospray ionization) MS, all LMW one-helix proteins from photosystem II were detected. In the four detected photosystem II supercomplexes of Nicotiana tabacum wild-type plants, 11 different one-helix proteins were identified as PsbE, -F, -H, -I, -K, -L, -M, -Tc, -W, and two isoforms of PsbX. The proteins PsbJ, -Y1, and -Y2 were localized in the buffer front after blue native (BN) PAGE, indicating their release during solubilization. Assembled PsbW is detected exclusively in supercomplexes, whereas it is absent in photosystem II core complexes, corroborating the protein's function for assembly of the light-harvesting complexes. This approach will substantiate gel-blot immunoanalysis for localization and identification of LMW protein subunits in any membrane protein complex.
authors.affiliation: Department für Biologie I, Ludwig Maximilians Universität, 82152 Planegg-Martinsried, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Granvogl
authors.forename: Mikael
authors.initials: M
authors.lastname: Zoryan
authors.forename: Matthias
authors.initials: M
authors.lastname: Plöscher
authors.forename: Lutz Andreas
authors.initials: LA
authors.lastname: Eichacker
mesh_terms: D000595:Amino Acid Sequence; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D036103:Nanotechnology; D009930:Organic Chemicals / Q000737:chemistry; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D012997:Solvents / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D020524:Thylakoids / Q000737:chemistry; D014026:Nicotiana / Q000166:cytology / Q000201:enzymology*
chemical_list: D008565:Membrane Proteins; D009930:Organic Chemicals; D045332:Photosystem II Protein Complex; D012997:Solvents