CONSEQUENCES FOR THE ORGANIZATION OF REACTION CENTER-LIGHT-HARVESTING-ANTENNA-1 (LH1) CORE COMPLEXES OF RHODOBACTER-SPHAEROIDES ARISING FROM DELETION OF AMINO-ACID-RESIDUES FROM THE C-TERMINUS OF THE LH1-ALPHA-POLYPEPTIDE
P. Mcglynn et al., CONSEQUENCES FOR THE ORGANIZATION OF REACTION CENTER-LIGHT-HARVESTING-ANTENNA-1 (LH1) CORE COMPLEXES OF RHODOBACTER-SPHAEROIDES ARISING FROM DELETION OF AMINO-ACID-RESIDUES FROM THE C-TERMINUS OF THE LH1-ALPHA-POLYPEPTIDE, The Journal of biological chemistry, 271(6), 1996, pp. 3285-3292
The light harvesting antenna 1 (LH1) complex of Rhodobacter sphaeroide
s is intimately associated with the reaction center (RC) as part of th
e reaction center RC-LH1 core complex, The pufA gene has been modified
such that between 5 and 16 amino acid residues were progressively del
eted from the C terminus of the LH1 alpha polypeptide. The two largest
deletions produced strains which were deficient in LH1, The remaining
four deletion mutants exhibited significant reductions in the average
level of LH1 per reaction center, Analysis of detergent-solubilized c
ores on sucrose gradients showed that the mutant strains had a sizeabl
e population of antenna-deficient reaction centers in addition to core
complexes with a reduced ratio of LH1:RC. The decrease in the ratio o
f LH1:RC in core complexes of the mutant strains was accompanied by a
progressive blue shift of the absorbance maximum of LH1, which we attr
ibute to the reduced aggregation state of LH1 in the smaller cores, Th
e PufX polypeptide was not required for photosynthetic growth in mutan
ts with reduced core sizes, We conclude that the level of LH1 in the b
acterial membrane, and the aggregation state of LH1 in core complexes,
are both influenced by the C terminus of the alpha polypeptide, and w
e discuss possible models for the organization of the core complex in
Rb. sphaeroides.