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

Abstract

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, αβa, αβb and αβd, were identified from Rps. palustris grown under high- (7000 lux) or intermediate- (1000 lux) light conditions. At lower light (300 and 90 lux), αβb was absent, and the level of αβa was significantly reduced. Results show that αβa and αβb peptides form the high light B800-850 complex, whereas the low light LH2 complex is only composed of αβd 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.