Peroxisomes are apparently missing in Zellweger syndrome; nevertheless, some of the integral membrane proteins of the organelle are present. Their distribution was studied by immunofluorescence microscopy. In control fibroblasts, peroxisomes appeared as small dots. In Zellweger fibroblasts, the peroxisomal membrane proteins were located in unusual empty membrane structures of larger size. These results suggest that the primary defect in this disease may be in the mechanism for import of matrix proteins.

Membranes were isolated from highly purified peroxisomes, mitochondria, and rough and smooth microsomes of rat liver by the one-step Na2CO3 procedure described in the accompanying paper (1982, J. Cell Biol . 93 :97-102) . The polypeptide compositions of these membranes were determined by SDS PAGE and found to be greatly dissimilar . The peroxisomal membrane contains 12% of the peroxisomal protein and consists of three major polypeptides (21,700, 67,700 and 69,700 daltons) as well as some minor polypeptides . The major peroxisomal membrane proteins as well as most of the minor ones are absent from the endoplasmic reticulum (ER) . Conversely, most ER proteins are absent from peroxisomes.By electron microscopy, purified peroxisomal membranes are -6 .8 nm thick and have a typical trilaminar appearance . The phospholipid/protein ratio of peroxisomal membranes is -200 nmol/mg; the principal phospholipids are phosphatidyl choline and phosphatidyl ethanolamine, as in ER and mitochondrial membranes. In contrast to the mitochondria, peroxisomal membranes contain no cardiolipin . All the membranes investigated contain a polypeptide band with a molecular mass of 15,000 daltons. Whether this represents an exceptional common membrane protein or a coincidence is unknown. The implications of these results for the biogenesis of peroxisomes are discussed.Knowledge of the peroxisomal membrane's properties is essential to an understanding both of the organelle's functions and of its biogenesis . The membrane separates the peroxisomal contents from the cytosol and defines the peroxisomal interior as a distinct intracellular space. The permeability properties of the membrane determine to what extent the peroxisome functions as a separate biochemical compartment. Knowledge of how the membrane is formed is essential to an understanding of the biogenesis of the organelle as a whole. If the membrane is derived from some other intracellular membrane, for example the endoplasmic reticulum (ER) (as is widely assumed), then one might expect to see some similarity in composition between them . If, on the other hand, the peroxisomes exist as a separate intracellular compartment, as has recently been suggested (1), then the peroxisomal membrane needs to have no structural similarity to the ER . THE JOURNAL OF CELL BIOLOGY " VOLUME 93 APRIL 1982 103-110 ©The Rockefeller University Press -0021-9525/82/04/0103/08 $1 .00We have applied the newly-developed sodium carbonate procedure described in the accompanying paper (2) to isolate peroxisomal, mitochondrial, and ER membranes.' We have partially characterized these three membranes, and found that their polypeptide compositions are almost entirely different, but their phospholipid compositions are similar. Some of these results have appeared in abstract form (3, 4) .' Rat liver microsomes were subfractionated by isopycnic centrifugation in linear sucrose gradients according to Beaufay et al. (7). The fractions selected as the "rough microsomal fraction" have been shown by these authors to c...

The Woronin body is a dense-core vesicle specific to filamentous ascomycetes (Euascomycetes), where it functions to seal the septal pore in response to cellular damage. The HEX-1 protein self-assembles to form this solid core of the vesicle. Here, we solve the crystal structure of HEX-1 at 1.8 A, which provides the structural basis of its self-assembly. The structure reveals the existence of three intermolecular interfaces that promote the formation of a three-dimensional protein lattice. Consistent with these data, self-assembly is disrupted by mutations in intermolecular contact residues and expression of an assembly-defective HEX-1 mutant results in the production of aberrant Woronin bodies, which possess a soluble noncrystalline core. This mutant also fails to complement a hex-1 deletion in Neurospora crassa, demonstrating that the HEX-1 protein lattice is required for Woronin body function. Although both the sequence and the tertiary structure of HEX-1 are similar to those of eukaryotic initiation factor 5A (eIF-5A), the amino acids required for HEX-1 self-assembly and peroxisomal targeting are absent in eIF-5A. Thus, we propose that a new function has evolved following duplication of an ancestral eIF-5A gene and that this may define an important step in fungal evolution.

Abstract. The rhoptry is an organelle of the malarial merozoite which has been suggested to play a role in parasite invasion of its host cell, the erythrocyte. A monoclonal antibody selected for reactivity with this organelle identifies a parasite synthesized protein Of 110 kD. From biosynthetic labeling experiments it was demonstrated that the protein is synthesized midway through the erythrocytic cycle (the trophozoite stage) but immunofluorescence indicates the protein is not localized in the organelle until the final stage (segmenter stage) of intraerythrocytic development. Immunoelectron microscopy shows that the protein is localized in the matrix of the rhoptry organelle and on membranous whorls secreted from the merozoite, mAb recognition of the protein is dithiothreitol (DTT) labile, indicating that the conformation of the epitope is dependent on a disulfide linkage. During erythrocyte reinvasion by the extraceUular merozoite, immunofluorescence shows the rhoptry protein discharging from the merozoite and spreading around the surface of the erythrocyte. The protein is located in the plasma membrane of the newly invaded erythrocyte. These studies suggest that the ll0-kD rhoptry protein is inserted into the membrane of the host erythrocyte during merozoite invasion.RYTHROCYTE invasion by the malarial merozoite is a multi-step process, initiated by receptor-mediated binding of the parasite to its host cell (9). Electron microscopic studies show that penetration of the erythrocyte by merozoites involves invagination of the erythrocyte membrane where the apical end of the merozoite contacts the host cell (1). A moving membrane junction is formed and the contact maintained while the merozoite is internalized into a vacuole, which eventually forms the parasitophorous vacuole. Intracellular development of the parasite occurs inside this vacuole. Although it is well documented that invasion occurs by erythrocyte membrane invagination, the biochemical mechanisms whereby the parasite induces such a profound alteration in the rigid membrane-cytoskeletal organization of the erythrocyte are not understood.Endocytosis is not observed in erythrocytes except in druginduced instances (25). It has been proposed that the malarial parasite must initiate the membrane changes by some heretofore unknown process. Implicated in this unusual process are the rhoptries, a pair of electron dense organelles found in plasmodia and in other closely related members of the apicomplexa which are obligate intracellular parasites.Rhoptries of Toxoplasma, Sarcocystis and Besnoitia species have all been implicated in the invasion process. In Toxoplasma, a penetration enhancement factor possessing lytic activity has been identified, and is believed to be secreted by the rhoptries during invasion (15). In plasmodia the rhoptries are club-shaped organelles located randomly in the cytoplasm in the preinvasive stages of the parasite, that appear to subtend ducts to the exterior of the apical portion of the merozoite at the time of invasion. Electro...

Bcl-w belongs to the prosurvival group of the Bcl-2 family, while the glutamate receptor δ2 (Grid2) is an excitatory receptor that is specifically expressed in Purkinje cells, and required for Purkinje cell synapse formation. A recently published result as well as our own findings have shown that Bcl-w can physically interact with an autophagy protein, Beclin1, which in turn has been shown previously to form a protein complex with the intracellular domain of Grid2 and an adaptor protein, nPIST. This suggests that Bcl-w and Grid2 might interact genetically to regulate mitochondria, autophagy, and neuronal function. In this study, we investigated this genetic interaction of Bcl-w and Grid2 through analysis of single and double mutant mice of these two proteins using a combination of histological and behavior tests. It was found that Bcl-w does not control the cell number in mouse brain, but promotes what is likely to be the mitochondrial fission in Purkinje cell dendrites, and is required for synapse formation and motor learning in cerebellum, and that Grid2 has similar phenotypes. Mice carrying the double mutations of these two genes had synergistic effects including extremely long mitochondria in Purkinje cell dendrites, and strongly aberrant Purkinje cell dendrites, spines, and synapses, and severely ataxic behavior. Bcl-w and Grid2 mutations were not found to influence the basal autophagy that is required for Purkinje cell survival, thus resulting in these phenotypes. Our results demonstrate that Bcl-w and Grid2 are two critical proteins acting in distinct pathways to regulate mitochondrial morphogenesis and control Purkinje cell dendrite development and synapse formation. We propose that the mitochondrial fission occurring during neuronal growth might be critically important for dendrite development and synapse formation, and that it can be regulated coordinately by multiple pathways including Bcl-2 and glutamate receptor family members.