Physiological and structural analysis of light-harvesting mutants of Rhodobacter sphaeroides

Abstract

Two mutants of Rhodobacter sphaeroides defective in formation of light-harvesting spectral complexes were examined in detail. Mutant RS103 lacked the B875 spectral complex despite the fact that substantial levels of the B875-oa polypeptide (and presumably the ,( polypeptide) were present. The B800-850 spectral complex was derepressed in RS103, even at high light intensities, and the growth rate was near normal at high light intensity but decreased relative to the wild type as the light intensity used for growth decreased. Mutant RS104 lacked colored carotenoids and the B800-850 spectral complex, as well as the cognate apoproteins. This strain grew normally at high light intensity and, as with RS103, the growth rate decreased as the light intensity used for growth decreased. At very low light intensities, however, RS104 would grow, whereas RS103 would not. Structural analysis of these mutants as well as others revealed that the morphology of the intracytoplasmic membrane invaginations is associated with the presence or absence of the B800-850 complex as well as of carotenoids. A low-molecular-weight intracytoplasmic membrane polypeptide, which may play a role in B800-850 complex formation, is described, as is a 62,000-dalton polypeptide whose abundance is directly related to light intensity as well as the absence of either of the light-harvesting spectral complexes. These data, obtained from studies of mutant strains and the wild type, are discussed in light of photosynthetic membrane formation and the abundance of spectral complexes per unit area of membrane. Finally, a method for the bulk preparation of the B875 complex from wild-type strain 2.4.1 is reported.

Posttranscriptional control of puc operon expression of B800-850 light-harvesting complex formation in Rhodobacter sphaeroides

“…The purified B800-850 complex in R. sphaeroides was found (23) not to be associated with a third polypeptide as observed for the purified B800-850 complex from Rhodobacter capsulatus (15). However, the polypeptide designated 15A, purified from the ICM of R. sphaeroides (6,7), is always absent in B800-850-strains of R. sphaeroides.…”

“…Since PUC-Pv showed no detectable B800-850 complexes under photoheterotrophic growth conditions despite the presence of the 0.5-kb pucBA-specific transcript (Fig. 9, lane 1), the possibility is raised that the polypeptides which comprise the B800-850 complex are synthesized but remain unassembled as we have shown for the B875 complex (9,23). Therefore, the presence of the B800-850-, polypeptide in PUC-Pv was examined by Western immunoblot analysis with antibody specific for the e polypeptide, designated 15B (6,7,23).…”

“…9, lane 1), the possibility is raised that the polypeptides which comprise the B800-850 complex are synthesized but remain unassembled as we have shown for the B875 complex (9,23). Therefore, the presence of the B800-850-, polypeptide in PUC-Pv was examined by Western immunoblot analysis with antibody specific for the e polypeptide, designated 15B (6,7,23). At the same time, the presence of another polypeptide, 15A (6,7,23), was also investigated in PUC-Pv as well as in PUC705-BA because the presence or absence of polypeptide 15A, although of unknown function, correlates with a B800-850+ phenotype, compared with the wild type (23).…”

“…Therefore, the presence of the B800-850-, polypeptide in PUC-Pv was examined by Western immunoblot analysis with antibody specific for the e polypeptide, designated 15B (6,7,23). At the same time, the presence of another polypeptide, 15A (6,7,23), was also investigated in PUC-Pv as well as in PUC705-BA because the presence or absence of polypeptide 15A, although of unknown function, correlates with a B800-850+ phenotype, compared with the wild type (23). Polypeptide 15A was previously purified and characterized by Cohen and Kaplan (6,7).…”

Membrane biogenesis in anoxygenic photosynthetic prokaryotes

“…Rb. sphaeroides mutants lacking LH 2 have been shown by the Niederman group (Hunter et al 1988) and in Sam Kaplan's laboratory (Kiley et al 1988) to form tubular rather than vesicular ICM, suggesting that LH 2 has a role in ICM morphogenesis. Kaplan et al (1983) have also shown that phospholipids, synthesized in the CM, are transferred to the ICM by an apparent phospholipid transfer protein at the time of cell division, while proteins and pigments are inserted into CM and ICM throughout the cell cycle.…”