ISOLATION AND CHARACTERIZATION OF SULFUR GLOBULE PROTEINS FROM CHROMATIUM-VINOSUM AND THIOCAPSA-ROSEOPERSICINA

Purple sulfur bacteria store sulfur as intracellular globules enclosed by a protein envelope. The proteins associated with sulfur globules o f Chromatium vinosum and Thiocapsa roseopersicina were isolated by ext raction into 50% aqueous acetonitrile containing 1% trifluoroacetic ac id and 10 mM dithiothreitol. The extracted proteins were separated by reversed-phase HPLC, revealing three major proteins from C. vinosum an d two from T. roseopersicina. All of these proteins have similar, rath er unusual amino acid compositions, being rich in glycine and aromatic amino acids, particularly tyrosine. The molecular masses of the C. vi nosum proteins were determined to be 10,498, 10,651, and 8,479 Da, whi le those from T. roseopersicina were found to be 10,661 and 8,759 Da b y laser desorption time-of-flight mass spectrometry. The larger T. ros eopersicina protein is N-terminally blocked, probably by acetylation, but small amounts of the unblocked form (mass = 10,619) were also isol ated by HPLC. Protein sequencing showed that the two larger C. vinosum proteins are homologous to each other and to the large T. roseopersic ina protein. The 8,479 Da C. vinosum and 8,759 Da T. roseopersicina si cina proteins are also homologous, indicating that sulfur globule prot eins are conserved between different species of purple sulfur bacteria .