N-Glycosylated mitochondrial proteins?

Iain Wilson WILSON at edv1.boku.ac.at
Tue Jul 4 09:02:50 EST 1995

> Is anything known about N-glycosylated proteins in mitochondria? I am
> worrying that mithochondria might contaminate my cell membrane
> preparation. But since most of my membrane proteins are N-glycosylated
> (since they bind conA) I would imagine that they are unlikely to be
> mitochondrial in origin? I guess I could assay some mitochondrial marker
> protein but would prefer to spend my time and resources more productively.
> The membrane prep is a standard homogenization/low speed/high speed
> centrifugation fraction.

There was some work which was concluded by the authors to indicate the 
presence of dolichyl-linked oligosaccharide biosynthesis in 
mitochondria. A quick check using Network Entrez linked to NCBI in the 
US and searching for dolichol and mitochondrial yields about 20 
abstracts. For instance:

J Biochem (Tokyo) 106: 133-8  (1989) [89380118]

Topological investigations. Study of the trypsin sensitivity of the N-
acetylglucosaminyl and mannosyl-transferase activities located in the outer
mitochondrial membrane.

C. Levrat, P. Louisot & R. Morelis

Department of Biochemistry, University of Lyon, INSERM-CNRS U. 189, France.

The trypsin sensitivity of the mitochondrial N-acetylglucosaminyl and
mannosyltransferase activities involved in the N-glycoprotein biosynthesis
through dolichol intermediates as well as the N-acetylglucosaminyl-transferase
activity involved in direct N-glycosylation were examined in mitochondria and
isolated outer mitochondrial membrane preparations. The trypsin action on
mitochondrial membrane was checked by measuring the activities of marker
enzymes (rotenone-insensitive NADH cytochrome c reductase, adenylate kinase,
and monoamine oxidase). Glycosyl-transferase activities of both N-glycosylation
pathways were insensitive to trypsin action and consequently were located in
the outer mitochondrial membrane. Based on the activator effect of the trypsin
on these enzyme activities, the results suggested two distinct orientations of
their active sites. As regards the N-glycoprotein biosynthesis pathway through
dolichol intermediates, the dolicholphosphoryl-mannose and dolichol-
pyrophosphoryl-di-N-acetylchitobiose synthases would be oriented outside while
the oligomannosyl-synthase and the oligomannosyl-transferase would be rather
oriented inside in the outer membrane. The N-acetylglucosaminyl-transferase
involved in the direct transfer of N-acetylglucosamine from its nucleotide
donor to a proteinic acceptor would be oriented outside in the outer membrane.

Whether this means that N-linked glycosylation of mitochondrial 
proteins occurs, I don't know.

Iain Wilson                        Institut fuer Chemie           
Tel: 43-1-47654-6065               Universitaet fuer Bodenkultur   
Fax: 43-1-310-5176                 Gregor-Mendel-Strasse 33
E-mail: wilson at edv1.boku.ac.at     A-1180, WIEN, Austria

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