Hex (β-hexosaminidase) is a soluble glycohydrolase involved in glycoconjugate degradation in lysosomes, however its localization has also been described in the cytosol and PM (plasma membrane). We previously demonstrated that Hex associated with human fibroblast PM as the mature form, which is functionally active towards GM2 ganglioside. In the present study, Hex was analysed in a lysosomal membrane-enriched fraction obtained by purification from highly purified human placenta lysosomes. These results demonstrate the presence of mature Hex associated with the lysosomal membrane and displaying, as observed for the PM-associated form, an acidic optimum pH. When subjected to sodium carbonate extraction, the enzyme behaved as a peripheral membrane protein, whereas Triton X-114 phase separation confirmed its partially hydrophilic nature, characteristics which are shared with the PM-associated form of Hex. Moreover, two-dimensional electrophoresis indicated a slight difference in the pI of β-subunits in the membrane and the soluble forms of the lysosomal Hex. These results reveal a new aspect of Hex biology and suggest that a fully processed membrane-associated form of Hex is translocated from the lysosomal membrane to the PM by an as yet unknown mechanism. We present a testable hypothesis that, at the cell surface, Hex changes the composition of glycoconjugates that are known to be involved in intercellular communication and signalling.
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Research Article|
September 10 2008
Identification and characterization of mature β-hexosaminidases associated with human placenta lysosomal membrane
Alessandro Magini;
Alessandro Magini
1
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
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Simona Mencarelli;
Simona Mencarelli
1
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
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Brunella Tancini;
Brunella Tancini
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
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Virginia Ciccarone;
Virginia Ciccarone
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
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Lorena Urbanelli;
Lorena Urbanelli
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
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Andrej Hasilik;
Andrej Hasilik
‡Institut fur Physiologische Chemie, Philipps-University Marburg, Karl-von-Frisch-Strasse 1, 35033 Marburg, Germany
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Carla Emiliani
Carla Emiliani
2
*Department of Experimental Medicine and Biochemical Sciences, University of Perugia, via del Giochetto, 06126 Perugia, Italy
2To whom correspondence should be addressed (email [email protected]).
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Publisher: Portland Press Ltd
Received:
June 19 2008
Accepted:
June 30 2008
Accepted Manuscript online:
June 30 2008
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© The Authors Journal compilation © 2008 Biochemical Society
2008
Biosci Rep (2008) 28 (4): 229–237.
Article history
Received:
June 19 2008
Accepted:
June 30 2008
Accepted Manuscript online:
June 30 2008
Citation
Alessandro Magini, Simona Mencarelli, Brunella Tancini, Virginia Ciccarone, Lorena Urbanelli, Andrej Hasilik, Carla Emiliani; Identification and characterization of mature β-hexosaminidases associated with human placenta lysosomal membrane. Biosci Rep 1 August 2008; 28 (4): 229–237. doi: https://doi.org/10.1042/BSR20080075
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