No abstract

Manganese is recruited in microorganisms by way of ABC-type transporter systems. Here, the expression, puri®cation and preliminary crystallographic analysis of a soluble form of the MntC solutebinding protein component of the MntABC manganese-import system from the cyanobacterium Synechococystis sp. PCC 6803 is reported. The protein (321 amino-acid residues) was expressed exclusively in inclusion bodies, which required unfolding and refolding in the presence of manganese prior to puri®cation. The puri®ed protein was crystallized in the presence of PEG and zinc. The crystals belong to space group P6 2 22, with unit-cell parameters a = b = 128.1, c = 90.0 A Ê and a single molecule in the asymmetric unit. The crystals diffract to 2.6 A Ê under cryoconditions using synchrotron radiation.

We have recently reported the crystallization of the reaction center of Photosystem II in the presence of detergent mixtures [Adir N (1999) Acta Crystallogr D Biol Crystallogr D55: 891-894]. We have used high performance liquid chromatography, dynamic light scattering, native gel electrophoresis and thermoluminescence measurements to characterize the interaction between these detergent mixtures and RC II, to try and understand their role in the crystallization process. Size exclusion HPLC and dynamic light scattering confirmed that the isolated RC II used for crystallization was exclusively monomeric. Dynamic light scattering measurements show that the detergent mixtures formed single micelles within a limited range of hydrodynamic radii. Both size exclusion HPLC and dynamic light scattering were used to follow the interaction between the detergent mixtures and monomeric RC II. These techniques revealed a decrease in the detergent mixture treated RC II particle size (with respect with the untreated RC II), and that RC II from solubilized crystals contained particles of the same size. Native gel electrophoresis showed that this change in apparent size is not due to the disintegration of the internal structure of the RC II complex. Thermoluminescence measurements of solubilized RC II crystals showed charge recombination from the S(2,3)Q(A) (-) state, indicating that RC II remains functionally viable following detergent mixture treatment and crystallization. The role of the detergent mixtures in the crystallization of RC II is discussed.

No abstract

AlvinFd sub-family is Pseudomonas aeruginosa Fd (PaFd), which also shows the above unusual redox properties. The PaFd structure has been determined to 1.32 resolution, the highest up to now for the AlvinFd sub-family. The detailed structural information that this structure affords, i.e. the precise geometry of the [4Fe-4S] clusters combined with the conformation of the surrounding residues and the electrostatic properties of the protein around and between the two clusters, the EPR spectroscopy studies, as well as a thorough comparison with existing high resolution structures of [4Fe-4S]containing proteins, provide structural reasons for the unusual redox properties of the Alvin-like 2[4Fe-4S] Fds.