Biomedical subjects

Michael R Jones

Publications and source records attributed to Michael R Jones.

24 records · Page 2Linked to original sources

PubMed2003

Type I photosynthetic reaction centres: structure and function.

We review recent advances in the study of the photosystem I reaction centre, following the determination of a spectacular 2.5 A resolution crystal structure for this complex of Synechococcus elongatus. Photosystem I is proving different to type II reaction centres in structure and organization, and the mechanism of transmembrane electron transfer, and is providing insights into the control of function in reaction centres that operate at very low redox potentials. The photosystem I complex of oxygenic organisms has a counterpart in non-oxygenic bacteria, the strictly anaerobic phototrophic green sulphur bacteria and heliobacteria. The most distinctive feature of these type I reaction centres is that they contain two copies of a large core polypeptide (i.e. a homodimer), rather than a heterodimeric arrangement of two related, but different, polypeptides as in the photosystem I complex. To compare the structural organization of the two forms of type I reaction centre, we have modelled the structure of the central region of the reaction centre from green sulphur bacteria, using sequence alignments and the structural coordinates of the S. elongatus Photosystem I complex. The outcome of these modelling studies is described, concentrating on regions of the type I reaction centre where important structure-function relationships have been demonstrated or inferred.

Amino Acid Sequence↗

PubMed2002

Insights into the evolution of the antenna domains of Type-I and Type-II photosynthetic reaction centres through homology modelling.

The (bacterio)chlorophylls of photosynthetic antenna and reaction centre complexes are bound to the protein via a fifth, axial ligand to the central magnesium atom. A number of the amino acids identified as providing such ligands are conserved between the large antenna of the cyanobacterial Type-I reaction centre and smaller antennas of the Type-I reaction centres of green sulphur bacteria and heliobacteria, and these numbers match closely the estimated number of antenna bacteriochlorophylls in the latter. The possible organisation of the antenna in the latter reaction centres is discussed, as is the mechanism by which the more pigment-rich antenna of the cyanobacterial reaction centre evolved. The homology modelling approach is also extended to the six-helix antenna proteins CP47 and CP43 associated with the Photosystem II reaction centre.

Amino Acid Sequence↗

PubMed2002

Protein-lipid interactions in the purple bacterial reaction centre.

The purple bacterial reaction centre uses the energy of sunlight to power energy-requiring reactions such as the synthesis of ATP. During the last 20 years, a combination of X-ray crystallography, spectroscopy and mutagenesis has provided a detailed insight into the mechanism of light energy transduction in the bacterial reaction centre. In recent years, structural techniques including X-ray crystallography and neutron scattering have also been used to examine the environment of the reaction centre. This mini-review focuses on recent studies of the surface of the reaction centre, and briefly discusses the importance of the specific protein-lipid interactions that have been resolved for integral membrane proteins.

Cardiolipins↗

PubMed2002

Tuning of the redox potential of the primary electron donor in reaction centres of purple bacteria: effects of amino acid polarity and position.

Mutation of residues His L168 and Phe M197 in the reaction centre from Rhodobacter sphaeroides has an unusually strong effect on the mid-point redox potential (E(m)) of the pair of bacteriochlorophylls that form the primary donor of electrons, tuning E(m) over a range of nearly 250 mV. This effect is correlated to the accompanying change in the permanent dipole of the L168 or M197 residue, suggesting it is mediated by changes in charge-dipole interactions. Comparisons with mutations made at a variety of other positions show that this correlation is particular to this residue pair, perhaps reflecting their proximity to the ring I regions of the dimer bacteriochlorophylls that form the overlap region between these molecules.

Amino Acids↗

PubMed2002

Tuning of the optical and electrochemical properties of the primary donor bacteriochlorophylls in the reaction centre from Rhodobacter sphaeroides: spectroscopy and structure.

A series of mutations have been introduced at residue 168 of the L-subunit of the reaction centre from Rhodobacter sphaeroides. In the wild-type reaction centre, residue His L168 donates a strong hydrogen bond to the acetyl carbonyl group of one of the pair of bacteriochlorophylls (BChl) that constitutes the primary donor of electrons. Mutation of His L168 to Phe or Leu causes a large decrease in the mid-point redox potential of the primary electron donor, consistent with removal of this strong hydrogen bond. Mutations to Lys, Asp and Arg cause smaller decreases in redox potential, indicative of the presence of weak hydrogen bond and/or an electrostatic effect of the polar residue. A spectroscopic analysis of the mutant complexes suggests that replacement of the wild-type His residue causes a decrease in the strength of the coupling between the two primary donor bacteriochlorophylls. The X-ray crystal structure of the mutant in which His L168 has been replaced by Phe (HL168F) was determined to a resolution of 2.5 A, and the structural model of the HL168F mutant was compared with that of the wild-type complex. The mutation causes a shift in the position of the primary donor bacteriochlorophyll that is adjacent to residue L168, and also affects the conformation of the acetyl carbonyl group of this bacteriochlorophyll. This conformational change constitutes an approximately 27 degrees through-plane rotation, rather than the large into-plane rotation that has been widely discussed in the context of the HL168F mutation. The possible structural basis of the altered spectroscopic properties of the HL168F mutant reaction centre is discussed, as is the relevance of the X-ray crystal structure of the HL168F mutant to the possible structures of the remaining mutant complexes.

Bacteriochlorophylls↗

PubMed2002

Reaction centres: the structure and evolution of biological solar power.

Reaction centres are complexes of pigment and protein that convert the electromagnetic energy of sunlight into chemical potential energy. They are found in plants, algae and a variety of bacterial species, and vary greatly in their composition and complexity. New structural information has highlighted features that are common to the different types of reaction centre and has provided insights into some of the key differences between reaction centres from different sources. New ideas have also emerged on how contemporary reaction centres might have evolved and on the possible origin of the first chlorophyll-protein complexes to harness the power of sunlight.

Bacterial Physiological Phenomena↗