Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.21 (beta-glucosidase)
 3,280 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explain the different secretion kinetics of lysosomal enzymes in Dictyostelium discoideum, previous investigators have hypothesized the existence of a heterogeneous population of lysosomes containing either the enzyme acid phosphatase or other hydrolase enzymes. This proposal predicts that at least two targeting mechanisms exist for lysosomal enzymes in this organism. To begin to investigate this possibility, the transport, processing, and targeting of acid phosphatase was studied by using a combination of radiolabel pulse-chase procedures, subcellular fractionations, and indirect immunofluorescence microscopy. Acid phosphatase was initially synthesized in axenically growing cells as a 56-kDa precursor polypeptide that was proteolytically processed after 20 min to a 55-kDa mature protein. This enzyme was rapidly transported from the endoplasmic reticulum to Golgi complex (halftime of 3 min) as measured by the acquisition of resistance to the enzyme endoglycosidase H. Furthermore, Percoll gradient fractionations indicated that radiolabeled forms of acid phosphatase reached dense lysosomal vesicles at about the same time as final processing was occurring. Proper sorting of acid phosphatase in D. discoideum apparently was not critically dependent on low intravacuolar pH since the addition of ammonium chloride did not stimulate the missorting and secretion of acid phosphatase. These results are very similar to previous observations concerning other Dictyostelium lysosomal enzymes. Consistent with the existence of a heterogeneus population of lysosomes, the percentage of radiolabeled acid phosphatase secreted 4 h into a chase period was 15-fold lower as compared with another lysosomal enzyme, beta-glucosidase. However, acid phosphatase, alpha-mannosidase, and beta-glucosidase were all predominantly colocalized as determined by indirect immunofluorescence, which for the first time demonstrates the homogeneous nature of the lysosomal system in D. discoideum. Taken together these results suggest that the processing and transport of acid phosphatase may be similar in nature to the glycosidases. However, the different kinetics of secretion of acid phosphatase versus the colocalized glycosidase enzymes suggests that an undefined mechanism operates to distinguish these classes of enzymes at a step after localization to lysosomes but prior to secretion.
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PMID:Processing, transport, and secretion of the lysosomal enzyme acid phosphatase in Dictyostelium discoideum. 265 46

The developmentally regulated Dictyostelium discoideum lysosomal enzyme beta-glucosidase is synthesized as a membrane-associated glycosylated precursor polypeptide which undergoes at least two proteolytic cleavage events to generate a soluble mature lysosomally localized protein. To begin to analyze the mechanisms regulating the sorting of this protein and the regulation during development of the expression of the encoding gene, we have cloned and sequenced a 2.6-kilobase (kb) cDNA which contains a complete 2463-nucleotide open reading frame coding for beta-glucosidase. Conceptual translation of this open reading frame predicts a polypeptide similar in molecular mass to the primary translation product of 94 kDa that also contains the same amino acid sequences of two V8 protease derived-peptides generated from the purified beta-glucosidase enzyme. The D. discoideum enzyme contained regions highly homologous at the amino acid sequence level to both bacterial and fungal beta-glucosidases, although these regions did not overlap. A potential cleavable signal sequence was also found in the first 21 amino acids followed by a highly polar stretch of 49 amino acids which (based on amino acid sequencing of the mature beta-glucosidase) represents a pro region for this protein. This region is similar in location, size, and charge to the D. discoideum alpha-mannosidase pro-I region (Schatzle, J., Bush, J., and Cardelli, J. (1992) J. Biol. Chem. 267, 4000-4007). Several small hydrophobic stretches of amino acids were also distributed throughout the protein; however, no obvious transmembrane region(s) were identified which might explain the observed membrane association of the precursor protein. Finally, Northern blot analysis indicated that the gene encoding this enzyme was under developmental regulation. The steady state level of a 2.7-kb beta-glucosidase mRNA decreased significantly during the aggregation stage of development, from high levels during growth, and then increased in the form of a larger size 2.8-kb mRNA during the final stages of development.
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PMID:Molecular cloning and characterization of the full-length cDNA encoding the developmentally regulated lysosomal enzyme beta-glucosidase in Dictyostelium discoideum. 828 12