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Christopher J Law

Publications and source records attributed to Christopher J Law.

6 recordsLinked to original sources
PubMed2004

Interactions stabilizing the structure of the core light-harvesting complex (LH1) of photosynthetic bacteria and its subunit (B820).

Reconstitution experiments with a chemically synthesized core light-harvesting (LH1) beta-polypeptide analogue having 3-methylhistidine instead of histidine in the position that normally donates the coordinating ligand to bacteriochlorophyll (Bchl) have provided the experimental data needed to assign to B820 one of the two possible alphabeta.2Bchl pairs that are observed in the crystal structure of LH2 from Phaeospirillum (formerly Rhodospirillum) molischianum, the one with rings III and V of Bchl overlapping. Consistent with the assigned structure, experimental evidence is provided to show that significant stabilizing interactions for both the subunit complex (B820) and LH1 occur between the N-terminal regions of the alpha- and beta-polypeptides. On the basis of the results with the chemically synthesized polypeptides used in this study, along with earlier results with protease-modified polypeptides, mutants, and chemically synthesized polypeptides, the importance of a stretch of 9-13 amino acids at the N-terminal end of the alpha- and beta-polypeptides is underscored. A progressive loss of interaction with the LH1 beta-polypeptide was found as the first three N-terminal amino acids of the LH1 alpha-polypeptide were removed. The absence of the N-terminal formylmethionine (fMet), or conversion of the sulfur in this fMet to the sulfoxide, resulted in a decrease in LH1 formation. In addition to the removal of fMet, removal of the next two amino acids also resulted in a decrease in K(assoc) for B820 formation and nearly eliminated the ability to form LH1. It is suggested that the first three amino acids (fMetTrpArg) of the LH1 alpha-polypeptide of Rhodospirillum rubrum form a cluster that is most likely involved in close interaction with the side chain of His -18 (see Figure 1 for numbering of amino acids) of the beta-polypeptide. The results provide evidence that the folding motif of the alpha- and beta-polypeptides in the N-terminal region observed in crystal structures of LH2 is also present in LH1 and contributes significantly to stabilizing the complex.

Amino Acid Sequence↗
PubMed2003

Crystal structure of the RC-LH1 core complex from Rhodopseudomonas palustris.

The crystal structure at 4.8 angstrom resolution of the reaction center-light harvesting 1 (RC-LH1) core complex from Rhodopseudomonas palustris shows the reaction center surrounded by an oval LH1 complex that consists of 15 pairs of transmembrane helical alpha- and beta-apoproteins and their coordinated bacteriochlorophylls. Complete closure of the RC by the LH1 is prevented by a single transmembrane helix, out of register with the array of inner LH1 alpha-apoproteins. This break, located next to the binding site in the reaction center for the secondary electron acceptor ubiquinone (UQB), may provide a portal through which UQB can transfer electrons to cytochrome b/c1.

Apoproteins↗
PubMed2003

OmpF enhances the ability of BtuB to protect susceptible Escherichia coli cells from colicin E9 cytotoxicity.

The outer membrane (OM) vitamin B(12) receptor, BtuB, is the primary receptor for E group colicin adsorption to Escherichia coli. Cell death by this family of toxins requires the OM porin OmpF but its role remains elusive. We show that OmpF enhances the ability of purified BtuB to protect bacteria against the endonuclease colicin E9, demonstrating either that the two OM proteins form the functional receptor or that OmpF is recruited for subsequent translocation of the bacteriocin. While stable binary colicin E9-BtuB complexes could be readily shown in vitro, OmpF-containing complexes could not be detected, implying that OmpF association with the BtuB-colicin complex, while necessary, must be weak and/or transient in nature.

Bacterial Outer Membrane Proteins↗
PubMed2003

Interaction of bacteriochlorophyll with the LH1 and PufX polypeptides of photosynthetic bacteria: use of chemically synthesized analogs and covalently attached fluorescent probes.

The protein components of the reaction center (RC) and core light-harvesting (LH 1) complexes of photosynthetic bacteria have evolved to specifically, but non-covalently, bind bacteriochlorophyll (Bchl). The contribution to binding of specific structural elements in the protein and Bchl may be determined for the LH 1 complex because its subunit can be studied by reconstitution under equilibrium conditions. Important to the determination and utilization of such information is the characterization of the interacting molecular species. To aid in this characterization, a fluorescent probe molecule has been covalently attached to each of the LH 1 polypeptides. The fluorescent probes were selected for optimal absorption and emission properties in order to facilitate their unique excitation and to enable the detection of energy transfer to Bchl. Oregon Green 488 carboxylic acid and 7-diethylaminocoumarin-3-carboxylic acid seemed to fulfill these requirements. Each of these probes were utilized to derivatize the LH1 beta-polypeptide of Rhodobacter sphaeroides. It was demonstrated that the beta-polypeptides did not interact with each other in the absence of Bchl. When Bchl was present, the probe-labeled beta-polypeptides interacted with Bchl to form subunit-type complexes much as those formed with the native polypeptides. Energy transfer from the probe to Bchl occurred with a high efficiency. The alpha-polypeptide from LH 1 of Rb. sphaeroides and that from Rhodospirillum rubrum were also derivatized in the same manner. Since these polypeptides do not oligomerize in the absence of a beta-polypeptide, reversible binding of a single Bchl to a single polypeptide could be measured. Dissociation constants for complex formation were estimated. The relevance of these data to earlier studies of equilibria involving subunit complexes is discussed. Also involved in the photoreceptor complex of Rb. sphaeroides and Rhodobacter capsulatus is another protein referred to as PufX. Two large segments of this protein were chemically synthesized, one reproducing the amino acid sequence of the core segment predicted for Rb. sphaeroides PufX and the other reproducing the amino acid sequence predicted for the core segment of Rb. capsulatus PufX. Each polypeptide was covalently labeled with a fluorescent probe and tested for energy transfer to Bchl. Each was found to bind Bchl with an affinity similar to the affinity of the LH 1 polypeptides for Bchl. It is suggested that PufX binds Bchl and interacts with a Bchlcalpha-polypeptide component of LH 1 to truncate, or interupt, the LH 1 ring adjacent to the location of the Q(B) binding site of the RC.

Journal Article↗
PubMedDate not supplied

The structure and function of bacterial light-harvesting complexes.

The harvesting of solar radiation by purple photosynthetic bacteria is achieved by circular, integral membrane pigment-protein complexes. There are two main types of light-harvesting complex, termed LH2 and LH1, that function to absorb light energy and to transfer that energy rapidly and efficiently to the photochemical reaction centres where it is trapped. This mini-review describes our present understanding of the structure and function of the purple bacterial light-harvesting complexes.

Bacterial Proteins↗