Photosynthesis Research

, Volume 86, Issue 1, pp 81–100

On the Role of Basic Residues in Adapting the Reaction Centre–LH1 Complex for Growth at Elevated Temperatures in Purple Bacteria

  • Ashley J. Watson
  • Arwel V. Hughes
  • Paul K. Fyfe
  • Marion C. Wakeham
  • Kate Holden-Dye
  • Peter Heathcote
  • Michael R. Jones
Regular Paper

DOI: 10.1007/s11120-005-4047-x

Cite this article as:
Watson, A.J., Hughes, A.V., Fyfe, P.K. et al. Photosynth Res (2005) 86: 81. doi:10.1007/s11120-005-4047-x

Abstract

The purple photosynthetic bacterium Thermochromatium tepidum is a moderate thermophile, with a growth optimum of 48–50 °C. The X-ray crystal structure of the reaction centre from this organism has been determined, and compared with that from mesophilic bacteria such as Blastochloris viridis and Rhodobacter sphaeroides (Nogi T et al. (2000) Proc Natl Acad Sci USA 97: 13561–13566). Structural features that could contribute to the enhanced thermal stability of the Thermochromatium tepidum reaction centre were discussed, including three arginine residues exposed at the periplasmic side of the membrane that are not present in reaction centres from mesophilic organisms, and potentially could increase the affinity of the complex for the surrounding membrane. In the present report these arginine residues, plus a histidine identified from an extensive sequence alignment, were engineered into structurally homologous positions in the Rhodobacter sphaeroides reaction centre, and the effect on the thermal stability of the Rhodobacter sphaeroides complex was examined. We find that these residues do not enhance the thermal stability of the reaction centre, as assessed by absorbance spectroscopy of the bacteriochlorin cofactors in membrane-bound reaction centres. Possible roles of these residues in the Thermochromatium tepidum reaction centre are discussed, and it is proposed that they facilitate stronger binding of the reaction centre to the encircling LH1 antenna complex, through ionic interactions with acidic residues at the C-terminal end of the LH1 α-polypeptide. Such an interaction could enhance the stability of the so-called ‘RC–LH1 core’ complex that is formed between the reaction centre and the LH1 antenna, and which represents the minimal functional photosynthetic unit in all known purple photosynthetic bacteria. Stronger bonding interactions between the two complexes could also contribute to an increase in the rigidity of the photosynthetic membrane in Thermochromatium tepidum, in accord with the general finding that the cytoplasmic membrane from thermophilic eubacteria is less fluid than its counterpart in mesophilic bacteria.

Keywords

basic residuescore complexLH1 antennamutagenesisreaction centrethermal stability

Abbreviations

A

Acidiphilium

Ach

Allochromatium

BChl

bacteriochlorophyll

Bl.

Blastochloris

BPhe

bacteriopheophytin

CL

cardiolipin

DDM

dodecylmaltoside

LDAO

lauryldimethylamine oxide

β-OG

β-octylglucoside

PE

phosphatidyl ethanolamine

PG

phosphatidyl glycerol

Rb.

Rhodobacter

Rps.

Rhodopseudomonas

Rubisco

ribulose-1,5-bisphosphate carboxylase/oxygenase

Tch.

Thermochromatium

Copyright information

© Springer 2005

Authors and Affiliations

  • Ashley J. Watson
    • 1
  • Arwel V. Hughes
    • 1
  • Paul K. Fyfe
    • 1
    • 3
  • Marion C. Wakeham
    • 1
  • Kate Holden-Dye
    • 1
  • Peter Heathcote
    • 2
  • Michael R. Jones
    • 1
  1. 1.Department of Biochemistry, School of Medical SciencesUniversity of Bristol BristolUK
  2. 2.School of Biological Sciences, Queen MaryUniversity of LondonLondonUK
  3. 3.Division of Biological Chemistry and Molecular Microbiology, Faculty of Life SciencesUniversity of DundeeDundeeUK