Kii ALS dementia.

Epidemiological surveys in the foci of ALS of the Kii Peninsula of Japan started in the early 1960s. Continuous surveys conducted for decades revealed that there have been two foci in the Kii Peninsula: one in Kozagawa in the southern part, and the other in Hobara in the south-east. Clinically, ALS patients of the Kii foci occasionally showed parkinsonian features or dementia that have not been reported in the sporadic form of ALS. Neuropathologically, numerous NFT that are identical to those of Alzheimer's disease were observed in the cerebral cortex and in the brainstem nuclei. To elucidate the etiopathogenesis of this unique form of ALS, an analysis was conducted of the environment in the focus areas and of the specimens from the patients with ALS. It was hypothesized that the long exposure of these environments to low calcium and magnesium, and an excess of aluminum and manganese in the drinking water and the soil, might lead to the deposition of some trace elements in the CNS, eventually causing neuronal degeneration and death.

Effects of site-directed mutagenesis on structure and function of recombinant rat liver S-adenosylhomocysteine hydrolase. Crystal structure of D244E mutant enzyme.

A site-directed mutagenesis, D244E, of S-adenosylhomocysteine hydrolase (AdoHcyase) changes drastically the nature of the protein, especially the NAD(+) binding affinity. The mutant enzyme contained NADH rather than NAD(+) (Gomi, T., Takata, Y., Date, T., Fujioka, M., Aksamit, R. R., Backlund, P. S., and Cantoni, G. L. (1990) J. Biol. Chem. 265, 16102-16107). In contrast to the site-directed mutagenesis study, the crystal structures of human and rat AdoHcyase recently determined have shown that the carboxyl group of Asp-244 points in a direction opposite to the bound NAD molecule and does not participate in any hydrogen bonds with the NAD molecule. To explain the discrepancy between the mutagenesis study and the x-ray studies, we have determined the crystal structure of the recombinant rat-liver D244E mutant enzyme to 2.8-A resolution. The D244E mutation changes the enzyme structure from the open to the closed conformation by means of a approximately 17 degrees rotation of the individual catalytic domains around the molecular hinge sections. The D244E mutation shifts the catalytic reaction from a reversible to an irreversible fashion. The large affinity difference between NAD(+) and NADH is mainly due to the enzyme conformation, but not to the binding-site geometry; an NAD(+) in the open conformation is readily released from the enzyme, whereas an NADH in the closed conformation is trapped and cannot leave the enzyme. A catalytic mechanism of AdoHcyase has been proposed on the basis of the crystal structures of the wild-type and D244E enzymes.

Mechanisms for auto-inhibition and forced product release in glycine N-methyltransferase: crystal structures of wild-type, mutant R175K and S-adenosylhomocysteine-bound R175K enzymes.

Glycine N-methyltransferase (S-adenosyl-l-methionine: glycine methyltransferase, EC 2.1.1.20; GNMT) catalyzes the AdoMet-dependent methylation of glycine to form sarcosine (N-methylglycine). Unlike most methyltransferases, GNMT is a tetrameric protein showing a positive cooperativity in AdoMet binding and weak inhibition by S-adenosylhomocysteine (AdoHcy). The first crystal structure of GNMT complexed with AdoMet showed a unique "closed" molecular basket structure, in which the N-terminal section penetrates and corks the entrance of the adjacent subunit. Thus, the apparent entrance or exit of the active site is not recognizable in the subunit structure, suggesting that the enzyme must possess a second, enzymatically active, "open" structural conformation. A new crystalline form of the R175K enzyme has been grown in the presence of an excess of AdoHcy, and its crystal structure has been determined at 3.0 A resolution. In this structure, the N-terminal domain (40 amino acid residues) of each subunit has moved out of the active site of the adjacent subunit, and the entrances of the active sites are now opened widely. An AdoHcy molecule has entered the site occupied in the "closed" structure by Glu15 and Gly16 of the N-terminal domain of the adjacent subunit. An AdoHcy binds to the consensus AdoMet binding site observed in the other methyltransferase. This AdoHcy binding site supports the glycine binding site (Arg175) deduced from a chemical modification study and site-directed mutagenesis (R175K). The crystal structures of WT and R175K enzymes were also determined at 2.5 A resolution. These enzyme structures have a closed molecular basket structure and are isomorphous to the previously determined AdoMet-GNMT structure. By comparing the open structure to the closed structure, mechanisms for auto-inhibition and for the forced release of the product AdoHcy have been revealed in the GNMT structure. The N-terminal section of the adjacent subunit occupies the AdoMet binding site and thus inhibits the methyltransfer reaction, whereas the same N-terminal section forces the departure of the potentially potent inhibitor AdoHcy from the active site and thus facilitates the methyltransfer reaction. Consequently GNMT is less active at a low level of AdoMet concentration, and is only weakly inhibited by AdoHcy. These properties of GNMT are particularly suited for regulation of the cellular AdoMet/AdoHcy ratio.

Crystallization and preliminary x-ray diffraction studies of guanidinoacetate methyltransferase from rat liver.

Guanidinoacetate methyltransferase is the enzyme which catalyzes the last step of creatine biosynthesis. The enzyme is found ubiquitously and in abundance in the livers of all vertebrates. Recombinant rat-liver guanidinoacetate methyltransferase has been crystallized with guanidinoacetate and S-adenosylhomocysteine. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 54.8, b = 162.5, c = 56.1 A, beta = 96.8 (1) degrees at 93 K, and typically diffract beyond 2.8 A.

Crystal structure of S-adenosylhomocysteine hydrolase from rat liver.

The crystal structure of rat liver S-adenosyl-L-homocysteine hydrolase (AdoHcyase, EC 3.3.1.1) which catalyzes the reversible hydrolysis of S-adenosylhomocysteine (AdoHcy) has been determined at 2.8 A resolution. AdoHcyase from rat liver is a tetrameric enzyme with 431 amino acid residues in each identical subunit. The subunit is composed of the catalytic domain, the NAD+-binding domain, and the small C-terminal domain. Both catalytic and NAD+-binding domains are folded into an ellipsoid with a typical alpha/beta twisted open sheet structure. The C-terminal section is far from the main body of the subunit and extends into the opposite subunit. An NAD+ molecule binds to the consensus NAD+-binding cleft of the NAD+-binding domain. The peptide folding pattern of the catalytic domain is quite similar to the patterns observed in many methyltransferases. Although the crystal structure does not contain AdoHcy or its analogue, there is a well-formed AdoHcy-binding crevice in the catalytic domain. Without introducing any major structural changes, an AdoHcy molecule can be placed in the catalytic domain. In the structure described here, the catalytic and NAD+-binding domains are quite far apart from each other. Thus, the enzyme appears to have an "open" conformation in the absence of substrate. It is likely that binding of AdoHcy induces a large conformational change so as to place the ribose moiety of AdoHcy in close proximity to the nicotinamide moiety of NAD+. A catalytic mechanism of AdoHcyase has been proposed on the basis of this crystal structure. Glu155 acts as a proton acceptor from the O3'-H when the proton of C3'-H is abstracted by NAD+. His54 or Asp130 acts as a general acid-base catalyst, while Cys194 modulates the oxidation state of the bound NAD+. The polypeptide folding pattern of the catalytic domain suggests that AdoHcy molecules can travel freely to and from AdoHcyase and methyltransferases to properly regulate methyltransferase activities. We believe that the crystal structure described here can provide insight into the molecular architecture of this important regulatory enzyme.

Aluminum-induced model of motor neuron degeneration: subperineurial injection of aluminum in rabbits.

Environmental factors, particularly chronic exposure to aluminum (Al) and manganese (Mn) with dietary deficiency of calcium (Ca) and magnesium (Mg), are speculated to be contributory in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, the mechanisms by which these elements accumulate in the CNS tissues and induce neuronal death are not known. In the present study, we investigated the retrograde transport of Al as a possible mechanism of pathogenesis. Al (as aluminum chloride or maltol) was injected into the subepineurial space of the sciatic nerve with subsequent morphological evaluation of the neurotoxic effect on spinal motor neurons in rabbits. Spheroid/globules, central and peripheral chromatolysis, and neuronal degeneration were observed in the spinal anterior horn in Al-maltol, Al chloride, and maltol treated rabbits to more marked extent than those in uninjected or saline controls. By electron microscopy, the soma and dendrites of neurons in the anterior horn at the fifth lumbar spinal cord in the Al-treated rabbit showed marked edematous change, fragmentation of granular endoplasmic reticulum, increased accumulation of neurofilament, and accumulation of free ribosomes and lipid-droplet-like structures. Horseradish peroxidase (HRP) reactive product was seen in the axons and cytoplasm of Schwann cells of the sciatic nerve in Al-maltol treated rabbits, suggesting that the permeability of the blood-nerve-barrier was increased by injection of Al-maltol. We suggest that Al, subperineurially injected, was absorbed into the spinal cord and induced degeneration of spinal motor neurons in these rabbits. These findings indicate that the retrograde transport of Al into spinal motor neurons via the peripheral nervous system may exacerbate neuronal degeneration in ALS.

Infantile autism and Duchenne muscular dystrophy.

We report a boy with autism and Duchenne muscular dystrophy. Myopathy was noted after 2 years of age and has since progressed slowly. At present this autistic child, 11 years 4 months old, has shown no signs of deterioration.