The solution structure of Rhodobacter sphaeroides LH1β reveals two helical domains separated by a more flexible region: Structural consequences for the LH1 complex

Matthew J. Conroy, Willem H.J. Westerhuis, Pamela S. Parkes-Loach, Paul A. Loach, C. Neil Hunter, Michael P. Williamson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations

Abstract

Here, the solution structure of the Rhodobacter sphaeroides core light-harvesting complex β polypeptide solubilised in chloroform:methanol is presented. The structure, determined by homonuclear NMR spectroscopy and distance geometry, comprises two alpha helical regions (residue -34 to -15 and -11 to +6, using the numbering system in which the conserved histidine residue is numbered zero) joined by a more flexible four amino acid residue linker. The C-terminal helix forms the membrane spanning region in the intact LH1 complex, whilst the N-terminal helix must lie in the lipid head groups or in the cytoplasm, and form the basis of interaction with the α polypeptide. The structure of a mutant β polypeptide W+9F was also determined. This mutant, which is deficient in a hydrogen bond donor to the bacteriochlorophyll, showed an identical structure to the wild-type, implying that observed differences in interaction with other LH1 polypeptides must arise from cofactor binding. Using these structures we propose a modification to existing models of the intact LH1 complex by replacing the continuous helix of the β polypeptide with two helices, one of which lies at an acute angle to the membrane plane. We suggest that a key difference between LH1 and LH2 is that the β subunit is more bent in LH1. This modification puts the N terminus of LH1β close to the reaction centre H subunit, and provides a rationale for the different ring sizes of LH1 and LH2 complexes. (C) 2000 Academic Press.

Original languageEnglish (US)
Pages (from-to)83-94
Number of pages12
JournalJournal of Molecular Biology
Volume298
Issue number1
DOIs
StatePublished - Apr 21 2000

Keywords

  • Light-harvesting complex
  • Model
  • NMR
  • Rhodobacter sphaeroides
  • Transmembrane helix

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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