Characterization of LHI- and LHI+ Rhodobacter capsulatus pufA mutants

Abstract

The NH2 termini of light-harvesting complex I (LHI) polypeptides a and ,B of Rhodobacter caus are thought to be involved in the assembly of the LHI complex. For a more detailed study of the role of the NH2-terminal segment of the LHI a protein in insertion into the intracytoplasmic membrane (ICM) of R. ca,psulaus, amino acids 6 to 8, 9 to 11, 12 and 13, or The LHI a and 1 polypeptides are present in a 1:1 ratio. The LHI apoproteins are integral proteins of the intracytoplasmic membrane (ICM) and span the membrane once with * Corresponding author. a central hydrophobic domain (51-53). The NH2 terminus of the LHI a polypeptide is located in the cytoplasm and has a short hydrophobic central part of amino acid residues flanked by positively charged residues which are next to a conserved proline (51, 52). The LHI a protein is inserted into the ICM in wild-type amounts only in the presence of the LHI 1 protein (43). The LHI 1 protein, however, has a negatively charged NH2 terminus and is able to integrate temporarily into the membrane in the absence of the LHI a protein (43). The LHI 13 protein was observed to be inserted earlier into the ICM than was the LHI a protein (43).The described structures and features of the LHI a and 1 polypeptides are conserved among several species of the genus Rhodospirillaceae (50). Two highly conserved amino acid residues (Trp-8 and Pro-13) are present in the NH2 terminus of the LHI a polypeptide (50). The aromatic structure of the Trp at position 8 seems to be of importance for the insertion of the LHI a polypeptide into the ICM (42). The conservative amino acid residue Pro-13, however, seems to be necessary for keeping the LHI 1 partner polypeptide in the membrane (42).Deletions or insertions have been introduced into the NH2 terminus of the LHI a protein to obtain more information on the structural requirements for the membrane insertion of the LHI a protein and the assembly of both LHI proteins into a functional complex. The construction and characterization of R capsulatus LHI-strains containing a mutated LHI a polypeptide are described in this report. Additionally, LHI+ revertant strains of one LHI-mutant strain are characterized.3030

The role of pigments in the assembly of photosynthetic complexes in Rhodobacter capsulatus

“…Possibly they slip out of the membrane. Similar results have been obtained with strains mutated in the N-terminal domain of LHIa (RICHTER et al 1992). Under both conditions, mutation of the pigment-binding polypeptide or interruption of BChl synthesis, the pigment-protein complexes were not assembled and the ppolypeptide disappeared first from the membrane.…”

Photoprotection in a purple phototrophic bacterium mediated by oxygen-dependent alteration of carotenoid excited-state properties

“…There is evidence that the Trp residue of the highly conserved Lys-Ile-Trp (KIW) motif found in the N-terminal domain of the LH1α polypeptide plays a role in binding spheroidenone in the LH1 complex of Rba. capsulatus (45,46); however, the same KIW motif is found in LH2, and no ICT state is found in this complex. It is possible that the neighboring αTyr-27 residue provides the hydrogen bond to the C2 keto group of spheroidenone that stabilizes the s-trans configuration as the corresponding residue in LH2 is a Gly.…”

The Intracytoplasmic Membranes of Purple Bacteria - Assembly of Energy-Transducing Complexes

“…The duplicated nucleotides code for the amino acids Lys, Ile and Trp. The revertant LHI protein doubled its carotenoid content [Richter et al, 1992].…”