Cd(II)- and Pb(II)-Induced Self-Assembly of Peripheral Membrane Domains from Protein Kinase C.

Cd2+ and Pb2+ are xenobiotic heavy metal ions that use ionic mimicry to interfere with the cellular function of biomacromolecules. Using a combination of SAXS, electron microscopy, FRET, and solution NMR spectroscopy, we demonstrate that treatment with Cd2+ and Pb2+ causes self-assembly of protein kinase C regulatory domains that peripherally associate with membranes. The self-assembly process successfully competes with ionic mimicry and is mediated by conserved protein regions that are distinct from the canonical Ca2+-binding motifs of protein kinase C. The ability of protein oligomers to interact with anionic membranes is enhanced compared to the monomeric species. Our findings suggest that metal-ion-dependent peripheral membrane domains can be utilized for generating protein-metal-ion nanoclusters and serve as biotemplates for the design of sequestration agents.

Crystallization and preliminary X-ray diffraction analysis of 5,10- methylenetetrahydrofolate dehydrogenase/cyclohydrolase from Thermoplasma acidophilum DSM 1728.

The methylenetetrahydrofolate dehydrogenase/ cyclohydrolase (MTHFDC) from the thermoacidophilic archaeon Thermoplasma acidophilum is a 30.6 kDa molecular-mass enzyme that sequentially catalyzes the conversion of formyltetrahydrofolate to methylenetetrahydrofolate, with a preference for NADP as a cofactor, rather than NAD. In order to elucidate the functional and structural features of MTHFDC from archaeons at a molecular level, it was overexpressed in Escherichia coli and crystallized in the presence of its cofactor, NADP, at 295 K using polyethylene glycol (PEG) 4000 as a precipitant. The crystal is a member of the monoclinic space group P21, with the following unit cell parameters: a=66.333 A, b=52.868 A, c=86.099 A, and beta= 97.570o, and diffracts to a resolution of at least 2.40 A at the synchrotron. Assuming a dimer in the crystallographic asymmetric unit, the calculated Matthews parameter (VM) was 2.44 A3/Da and the solvent content was 49.7%.