Open AccessTransverse membrane topography of the B875 light-harvesting polypeptides of wild-type Rhodobacter sphaeroides
Author(s) -
Jon Y. Takemoto,
Ron L. Peterson,
Monier H. Tadros,
Gerhart Drews
Publication year - 1987
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.169.10.4731-4736.1987
Subject(s) - spheroplast , biology , proteinase k , biochemistry , vesicle , periplasmic space , rhodobacter sphaeroides , trypsin , peptide sequence , chlamydomonas , membrane , microbiology and biotechnology , biophysics , enzyme , mutant , escherichia coli , photosynthesis , gene
Purified B875 light-harvesting complex, chromatophores, and spheroplast-derived vesicles from wild-type Rhodobacter sphaeroides were treated with proteinase K or trypsin, and the alpha and beta polypeptides were analyzed by electrophoretic, immunochemical, and protein-sequencing methods. With the purified complex, proteinase K digested both polypeptides and completely eliminated the A875 peak. Trypsin digested the alpha polypeptide and reduced the A875 by 50%. Proteinase K cleaved the beta polypeptide of chromatophores and the alpha polypeptide of spheroplast-derived vesicles. Sequence analyses of polypeptides extracted from proteinase K-treated chromatophores revealed that the beta polypeptide was cleaved between amino acids 4 and 5 from the N terminus. The N terminus of the alpha polypeptide was intact. We concluded that the N terminus of the beta polypeptide is exposed on the cytoplasmic membrane surface, and the difference in the digestion patterns between the spheroplast-derived vesicles and chromatophores suggested that the C terminus of the alpha polypeptide is exposed on the periplasmic surface.