Biomedical subjects

M Duerring

Publications and source records attributed to M Duerring.

3 recordsLinked to original sources

PubMed1991

Isolation, crystallization, crystal structure analysis and refinement of constitutive C-phycocyanin from the chromatically adapting cyanobacterium Fremyella diplosiphon at 1.66 A resolution.

Constitutive phycocyanin from cyanobacterium Fremyella diplosiphon (Calothrix sp. PCC 7601) grown in green light, has been isolated and crystallized. The crystals belong to the space group R3 with cell constants a = b = 180.26 A, c = 61.24 A, alpha = beta = 90 degrees, gamma = 120 degrees. The crystal structure has been determined by Patterson search techniques using the molecular model of C-phycocyanin from the cyanobacterium Agmenellum quadruplicatum. The asymmetric unit of the crystal cell consists of two (alpha beta)-monomers related by a local dyad. Three asymmetric units are arranged around a crystallographic triad and form an (alpha beta)6-hexamer, the functional unit in the native antenna rod. The initial structure has been refined in a cyclic manner by energy-restrained crystallographic refinement and modelling until the conventional crystallographic R-factor converged at 18.1% with data to a resolution of 1.66 A. The molecular structure resembles closely the C-phycocyanins of Mastigocladus laminosus and A. quadruplicatum. The conformation and configuration of the alpha-84 and beta-84 chromophores is very similar to the corresponding chromophores in the trimeric C-phycocyanin of M. laminosus, whereas the beta-155 chromophore differs in configuration with C(4)-Z, C(10)-Z and C(15)-Z compared to C(4)-Z, C(10)-Z, C(15)-Z,E. The stereochemistry of the beta-155 chiral centres is C(2)-RC(3)-R and C(31)-S, respectively, whereas alpha-84 and beta-84 have C(2)-RC(3)-R and C(31)-R. The amino acid sequences of constitutive and inducible phycocyanin differ mainly in residues located on the surface of the beta-subunits that mediate the inter-hexameric contacts.

Amino Acid Sequence↗

PubMed1991

Role of electrostatic interaction in the stability of the hexamer of constitutive phycocyanin from Fremyella diplosiphon.

The role of electrostatic interactions between the charges carried by the titratable groups in the different aggregates of constitutive phycocyanin from Fremyella diplosiphon has been studied by using a simple theoretical approach based on the modified Tanford-Kirkwood model. The electrostatic potential has also been calculated by means of a numerical solution of the linearized Poisson-Boltzmann equations using the finite-differences technique. The pH dependence of the electrostatic contribution to free energy suggests an electrostatic stabilization of the alpha- and beta-subunits as well as of the (alpha beta)-monomer over a broad pH interval. The charge distributions in the individual alpha- and beta-subunits produce electrostatic complementarity and promote the assembly of the subunits to the (alpha beta)-monomer, as well as of the monomers to the larger trimeric and hexameric aggregates. Trimer-trimer electrostatic interactions exhibit strong pH dependence, predicting an association/dissociation equilibrium with a midpoint at pH 6. The electrostatic trimer-trimer interactions correspond to the steric fit, suggesting that electrostatic interactions may initially help to orient the trimers during aggregation. The distribution of the electrostatic potential of the monomers and of the higher aggregates suggests that it plays an important role also in phycocyanin-linker protein binding.

Computer Simulation↗

PubMed1990

Refined three-dimensional structure of phycoerythrocyanin from the cyanobacterium Mastigocladus laminosus at 2.7 A.

The structure of the phycobiliprotein phycoerythrocyanin from the thermophilic cyanobacterium Mastigocladus laminosus has been determined at 2.7 A resolution by X-ray diffraction methods on the basis of the molecular model of C-phycocyanin from the same organism. Hexagonal phycoerythrocyanin crystals of space group P6(3) with cell constants a = b = 156.86 A, c = 40.39 A, alpha = beta = 90 degrees, gamma = 120 degrees are almost isomorphous to C-phycocyanin crystals. The crystal structure has been refined by energy-restrained crystallographic refinement and model building. The conventional crystallographic R-factor of the final model was 19.2% with data to 2.7 A resolution. In phycoerythrocyanin, the three (alpha beta)-subunits are arranged around a 3-fold symmetry axis, as in C-phycocyanin. The two structures are very similar. After superposition, the 162 C alpha atoms of the alpha-subunit have a mean difference of 0.71 A and the 171 C alpha atoms of the beta-subunit differ by 0.51 A. The stereochemistry of the chiral atoms in the phycobiliviolin chromophore A84 is C(31)-R, C(4)-S. The configuration of the chromophore is C(10)-Z, C(15)-Z and the conformation C(5)-anti, C(9)-syn and C(14)-anti like the phycocyanobilin chromophores in phycoerythrocyanin and C-phycocyanin.

Computer Graphics↗