This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Richter, P Articles by Drews, G Search for Related Content PubMed PubMed Citation Articles by Richter, P Articles by Drews, G

 Previous Article  |  Next Article 

J Bacteriol. 1992 May; 174(9): 3030-3041

research-article

Characterization of LHI- and LHI+ Rhodobacter capsulatus pufA mutants.

Institut für Mikrobiologie, Albert-Ludwigs-Universität Freiburg, Germany.

ABSTRACT

The NH2 termini of light-harvesting complex I (LHI) polypeptides alpha and beta of Rhodobacter capsulatus are thought to be involved in the assembly of the LHI complex. For a more detailed study of the role of the NH2-terminal segment of the LHI alpha protein in insertion into the intracytoplasmic membrane (ICM) of R. capsulatus, amino acids 6 to 8, 9 to 11, 12 and 13, or 14 and 15 of the LHI alpha protein were deleted. Additionally, the hydrophobic stretch of the amino acids 7 to 11 was lengthened by insertion of hydrophobic or hydrophilic amino acids. All mutations abolished the ability of the mutant strains to form a functional LHI antenna complex. All changes introduced into the LHI alpha protein strongly reduced the stability of its LHI beta partner protein in the ICM. The effects on the mutated protein itself, however, were different. Deletion of amino acids 6 to 8, 9 to 11, or 14 and 15 drastically reduced the amount of the LHI alpha protein inserted into the membrane or prevented its insertion. Deletion of amino acids 12 and 13 and lengthening of the stretch of amino acids 7 to 11 reduced the half-life of the mutated LHI alpha protein in the ICM in comparison with the wild-type LHI alpha protein. Under the selective pressure of low light, revertants which regained a functional LHI antenna complex were identified only for the mutant strain deleted of amino acids 9 to 11 of the LHI alpha polypeptide [U43 (pTPR15)]. The restoration of the LHI+ phenotype was due to an in-frame duplication of 9 bp in the pufA gene directly upstream of the site of deletion present in strain U43(pTPR15). The duplicated nucleotides code for the amino acids Lys, Ile, and Trp. Membranes purified from the revertants were different from that of the reaction center-positive LHI+ LHII- control strain U43(pTX35) in doubling of the carotenoid content and increase of the size of the photosynthetic unit. By separating the reaction center and LHI complexes of the revertants by native preparative gel electrophoresis, we confirmed that the higher amount of carotenoids was associated with the LHI proteins.

This article has been cited by other articles:

• Lupo, D., Ghosh, R. (2004). The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants. J. Bacteriol. 186: 5585-5595 [Abstract] [Full Text]  
• Davis, C. M., Bustamante, P. L., Loach, P. A. (1995). Reconstitution of the Bacterial Core Light-harvesting Complexes of Rhodobacter sphaeroides and Rhodospirillum rubrum with Isolated alpha- and beta-Polypeptides, Bacteriochlorophyll a, and Carotenoid. J. Biol. Chem. 270: 5793-5804 [Abstract] [Full Text]