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Glycobiology Advance Access published online on September 30, 2009
Glycobiology, doi:10.1093/glycob/cwp156
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Human sialidase NEU4 long and short are extrinsic proteins bound to outer mitochondrial membrane and the endoplasmic reticulum, respectively

Alessandra Bigi1, Lavinia Morosi1, Chiara Pozzi1, Matilde Forcella1, Guido Tettamanti2, Bruno Venerando3, Eugenio Monti4 and Paola Fusi1

1 Department of Biotechnologies and Biosciences, University of Milan-Bicocca, Piazza della Scienza, 2, 20126, Milano
2 Laboratory of Stem Cells for Tissue Engineering, IRCCS Policlinico San Donato, 20097 San Donato Milanese
3 Department of Medical Chemistry, Biochemistry and Biotechnology, L.I.T.A.-Segrate, University of Milan, Via F.lli Cervi, 93, 20090 Segrate
4 Department of Biomedical Sciences and Biotechnology, University of Brescia, Viale Europa, 11, 25123 Brescia, Italy

Corresponding author: Paola Fusi, Department of Biotechnologies and Biosciences, University of Milan-Bicocca, Piazza della Scienza, 2, 20126, Milano. Phone: +390264483405; fax: +390264483565; e-mail: paola.fusi{at}unimib.it

Received on April 29, 2009; accepted on September 27, 2009

Sialidases are widely distributed glycohydrolytic enzymes removing sialic acid residues from glycoconjugates. In mammals, several sialidases with different subcellular localizations and biochemical features have been described. NEU4, the most recently identified member of the human sialidase family, is found in two forms, NEU4 long and NEU4 short, differing in the presence of a 12 aminoacid sequence at the N-terminus. Contradictory data are present in the literature about the subcellular distribution of these enzymes, their membrane anchoring mechanism being still unclear.

In this work we investigate human NEU4 long and NEU4 short membrane anchoring mechanism and their subcellular localization. Protein extraction with Triton X-114 and sodium carbonate and cross-linking experiments demonstrate that both forms of NEU4 are extrinsic membrane proteins, anchored via protein-protein interactions. Moreover, through confocal microscopy and subcellular fractionation, we show that the long form localizes in mitochondria, while the short form is also associated with the endoplasmic reticulum. Finally, mitochondria subfractionation experiments suggest that NEU4 long is bound to the outer mitochondrial membrane.

Key words: endoplasmic reticulum / long and short isoforms / mitochondrial membrane / peripheral membrane protein / sialidase NEU4


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