Characterisation of hydrophobic peptides by RP-HPLC from different spectral forms of LH2 isolated from Rps. palustris

The separation of light-harvesting peptides by RP-HPLC is notoriously difficult due to the typically strong interaction of peptides with the column matrix, their relatively low solubility in the mobile phase and the tendency for non-specific aggregation during sample preparation. This paper illustrates a reproducible method for investigating the composition of four spectrally different forms of LH2 isolated from Rps. palustris. The method contrasts with previous attempts to isolate peptides from these multi-LH2 complexes and uses the well characterised B800–850 complex from Rps. acidophila as a test of reliability. Three pairs of LH2 peptides, _a, _b and _d, were identified from Rps. palustris grown under high- (7000 lux) or intermediate- (1000 lux) light conditions. At lower light (300 and 90 lux), _b was absent, and the level of _a was significantly reduced. Results show that _a and _b peptides form the high light B800-850 complex, whereas the low light LH2 complex is only composed of _d peptides and resembles the B800–820 complex from Rps. acidophila by sequence homology. The absorption spectrum of this complex has a single peak centred on 800 nm and appears to be a novel LH2 complex. At low light growth conditions, this B800 species is the predominant LH2 complex in Rps. palustris and indicates that peptide expression is a crucial factor in adapting to different light intensities.