Progress in predicting protein function from structure: unique features of O-glycosidases.

The Structural Genomics Initiative promises to deliver between 10,000 and 20,000 new protein structures within the next ten years. One challenge will be to predict the functions of these proteins from their structures. Since the newly solved structures will be enriched in proteins with little sequence identity to those whose structures are known, new methods for predicting function will be required. Here we describe the unique structural characteristics of O-glycosidases, enzymes that hydrolyze O-glycosidic bonds between carbohydrates. O-glycosidase function has evolved independently many times and enzymes that carry out this function are represented by a large number of different folds. We show that O-glycosidases none-the-less have characteristic structural features that cross sequence and fold families. The electrostatic surfaces of this class of enzymes are particularly distinctive. We also demonstrate that accurate prediction of O-glycosidase function from structure is possible.

GABAergic neuroaxonal dystrophy and other cytopathological alterations in feline Niemann-Pick disease type C.

Feline Niemann-Pick disease type C (NPC) is an autosomal recessive lysosomal storage disease which shares many of the clinical, biochemical and pathological features of the corresponding human disorder. Cytopathological alterations in distinct neuronal cell populations were investigated in this animal model to gain a better understanding of the pathogenesis of brain dysfunction. Golgi and immunocytochemical methods were employed to characterize the cell architectural changes occurring in neuronal somata, dendrites and axons at different stages of disease progression. Cortical pyramidal neurons in laminae II, III, and V exhibited various degrees of meganeurite and/or swollen axon hillock formation with or without ectopic dendritogenesis. Enlarged axon hillock regions with neuritic processes and spines were recognized early in the progression of feline NPC but were less prevalent in mid to late stages of the disease. Glutamic acid decarboxylase (GAD) immunocytochemistry demonstrated immunoreactive spheroids in numerous GABAergic axons in neocortex, subcortical areas, and cerebellum. Parvalbumin-immunoreactive axonal spheroid distribution in brain closely mirrored results from the GAD studies, whereas calbindin D-28k-immunoreactive spheroids were conspicuously absent in most cortical and subcortical areas examined. Purkinje cell axonal spheroid formation progressed in a distal to proximal direction, with eventual involvement of recurrent axon collaterals. Purkinje cell death and a concomitant decrease in the numbers of spheroids in the cerebellum were observed late in the disease course. Clinical neurological signs in feline NPC occur in parallel with neuronal structural alterations and suggest that GABAergic neuroaxonal dystrophy is a contributor to brain dysfunction in this disease.

Feline sphingolipidosis resembling Niemann-Pick disease type C.

A 9-week old domestic short-hair kitten with progressive neurological dysfunction had histopathological lesions consistent with a lysosomal storage disease. Light microscopy of the brain, spinal cord, and ganglia revealed distention and vacuolation of many neuronal populations, and extensive neuroaxonal dystrophy. Large numbers of foamy macrophages were observed in the liver, spleen, lymph nodes, and lung. Hepatocytes appeared pale and swollen. Ultrastructural examination of all affected tissues and organs revealed heterogeneous membranous inclusions. Lipid analysis of liver revealed an excess of cholesterol, glucosylceramide, lactosylceramide and phospholipids including sphingomyelin. There was some increase in the levels of brain GM2 and GM3 gangliosides. Sphingomyelinase activity in liver was partially deficient or low normal. Skin fibroblasts were cultured from two affected cats from the colony established with littermates of the subject of this report. The cultured skin fibroblasts had partially decreased sphingomyelinase activity and a greatly decreased ability to esterify exogenous cholesterol. Clinical, morphological, and biochemical findings suggest that this cat had sphingolipidosis similar to human Niemann-Pick disease type C, a disease not previously described in the cat. The feline form of this storage disease may provide a useful model for studies on the human disease.