Tay-Sachs and Sandhoff diseases are lysosomal storage disorders that result from an inherited deficiency of beta-hexosaminidase A (alphabeta). Whereas the acute forms are associated with a total absence of hexosaminidase A and early death, the chronic adult forms exist with activity and protein levels of approximately 5%, and unaffected individuals have been found with only 10% of normal levels. Surprisingly, almost all disease-associated missense mutations do not affect the active site of the enzyme but, rather, inhibit its ability to obtain and/or retain its native fold in the endoplasmic reticulum, resulting in its retention and accelerated degradation. By growing adult Tay-Sachs fibroblasts in culture medium containing known inhibitors of hexosaminidase we have raised the residual protein and activity levels of intralysosomal hexosaminidase A well above the critical 10% of normal levels. A similar effect was observed in fibroblasts from an adult Sandhoff patient. We propose that these hexosaminidase inhibitors function as pharmacological chaperones, enhancing the stability of the native conformation of the enzyme, increasing the amount of hexosaminidase A capable of exiting the endoplasmic reticulum for transport to the lysosome. Therefore, pharmacological chaperones could provide a novel approach to the treatment of adult Tay-Sachs and possibly Sandhoff diseases.

The iron respiratory chain of the acidophilic bacterium Acidithiobacillus ferrooxidans involves various metalloenzymes. Here we demonstrate that the oxygen reduction pathway from ferrous iron (named downhill pathway) is organized as a supercomplex constituted of proteins located in the outer and inner membranes as well as in the periplasm. For the first time, the outer membrane-bound cytochrome c Cyc2 was purified, and we showed that it is responsible for iron oxidation and determined that its redox potential is the highest measured to date for a cytochrome c. The organization of metalloproteins inside the supramolecular structure was specified by protein-protein interaction experiments. The isolated complex spanning the two membranes had iron oxidase as well as oxygen reductase activities, indicating functional electron transfer between the first iron electron acceptor, Cyc2, and the Cu A center of cytochrome c oxidase aa 3 . This is the first characterization of a respirasome from an acidophilic bacterium. In Acidithiobacillus ferrooxidans, O 2 reduction from ferrous iron must be coupled to the energy-consuming reduction of NAD ؉ (P) from ferrous iron (uphill pathway) required for CO 2 fixation and other anabolic processes. Besides the proteins involved in the O 2 reduction, there were additional proteins in the supercomplex, involved in uphill pathway (bc complex and cytochrome Cyc 42 ), suggesting a possible physical link between these two pathways.

Alzheimer's disease (AD) is caused by the cerebral deposition of ␤-amyloid (A␤), a 38 -43-amino acid peptide derived by proteolytic cleavage of the amyloid precursor protein (APP). Initial studies indicated that final cleavage of APP by the ␥-secretase (a complex containing presenilin and nicastrin) to produce A␤ occurred in the endosomal/lysosomal system. However, other studies showing a predominant endoplasmic reticulum localization of the ␥-secretase proteins and a neutral pH optimum of in vitro ␥-secretase assays have challenged this conclusion. We have recently identified nicastrin as a major lysosomal membrane protein. In the present work, we use Western blotting and immunogold electron microscopy to demonstrate that significant amounts of mature nicastrin, presenilin-1, and APP are co-localized with lysosomal associated membrane protein-1 (cAMP-1) in the outer membranes of lysosomes. Furthermore, we demonstrate that these membranes contain an acidic ␥-secretase activity, which is immunoprecipitable with an antibody to nicastrin. These experiments establish APP, nicastrin, and presenilin-1 as resident lysosomal membrane proteins and indicate that ␥-secretase is a lysosomal protease. These data reassert the importance of the lysosomal/endosomal system in the generation of A␤ and suggest a role for lysosomes in the pathophysiology of AD.

Aquifex aeolicus is a hyperthermophilic, chemolithoautotrophic, hydrogen-oxidizing, and microaerophilic bacterium growing at 85°C. We have shown that it can grow on an H 2 /S°medium and produce H 2 S from sulfur in the later exponential phase. The complex carrying the sulfur reducing activity (electron transport from H 2 to S°) has been purified and characterized. It is a membranebound multiprotein complex containing a [NiFe] hydrogenase and a sulfur reductase connected via quinones. The sulfur reductase is encoded by an operon annotated dms (dimethyl sulfoxide reductase) that we have renamed sre and is composed of three subunits. Sequence analysis showed that it belongs to the Me 2 SO reductase molybdoenzyme family and is similar to the sulfur/polysulfide/thiosulfate/tetrathionate reductases. The study of catalytic properties clearly demonstrated that it can reduce tetrathionate, sulfur, and polysulfide, but cannot reduce Me 2 SO and thiosulfate, and that NADPH increases the sulfur reducing activity. To date, this is the first characterization of a supercomplex from a bacterium that couples hydrogen oxidation and sulfur reduction. The distinctive feature in A. aeolicus is the cytoplasmic localization of the sulfur reduction, which is in accordance with the presence of sulfur globules in the cytoplasm. Association of this sulfur-reducing complex with a hydrogen-oxygen pathway complex (hydrogenase I, bc 1 complex) in the membrane suggests that subcomplexes involved in respiratory chains in this bacterium are part of supramolecular organization.The production of biomass in extreme light-independent environments is energized by chemolithoautotrophic oxidation and reduction of inorganic compounds like elemental sulfur (S°), 2 hydrogen, and nitrate (1, 2). Sulfur and sulfur compounds are the most abundant sources of both electron acceptors and electron donors in extremophilic environments (like volcanic environments) and are used by many microorganisms to support growth (3-6). Reduction and oxidation of sulfur compounds (sulfate, sulfite, thiosulfate, organic sulfoxide, elemental sulfur, polysulfides, and organic disulfide) are vital processes for many bacteria and essential steps in the global sulfur cycle. Because of the multiple oxidation states of sulfur, the biochemistry and chemistry of this cycle are complex and still not completely understood (7,8). This problem is exacerbated by the reactivities of the sulfur species at various oxidation states toward each other (7). The ability to reduce elemental sulfur is mostly found among hyperthermophilic micro-organisms (Archaea and Bacteria) (8), the majority of which depend on S°reduc-tion for optimal growth. They use either molecular hydrogen or organic compounds as electron donors. It has been suggested that S°respiration is one of the earliest mechanisms for energy conservation, because the hyperthermophiles are the forms of life evolving the most slowly (9).The processes by which micro-organisms reduce S°to H 2 S are still unclear for most of them, and only few ...