Linked Life Data

17561962

Source:http://linkedlifedata.com/resource/pubmed/id/17561962

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
13
pubmed:dateCreated
2007-7-5
pubmed:abstractText
Sphingolipid activator proteins (SAPs), GM2 activator protein (GM2AP) and saposins (Saps) A-D are small, enzymatically inactive glycoproteins of the lysosome. Despite of their sequence homology, these lipid-binding and -transfer proteins show different specificities and varying modes of action. Water-soluble SAPs facilitate the degradation of membrane-bound glycosphingolipids with short oligosaccharide chains by exohydrolases at the membrane-water interface. There is strong evidence that degradation of endocytosed components of the cell membrane takes place at intraendosomal and intralysosomal membranes. The inner membranes of the lysosome differ from the limiting membrane of the organelle in some typical ways: the inner vesicular membranes lack a protecting glycocalix, and they are almost free of cholesterol, but rich in bis(monoacylglycero)phosphate (BMP), the anionic marker lipid of lysosomes. In this study, we prepared glycosylated Sap-B free of other Saps by taking advantage of the Pichia pastoris expression system. We used immobilized liposomes as a model for intralysosomal vesicular membranes to probe their interaction with recombinantly expressed Sap-B. We monitored this interaction using SPR spectroscopy and an independent method based on the release of radioactively labelled lipids from liposomal membranes. We show that, after initial binding, Sap-B disturbs the membrane structure and mobilizes the lipids from it. Lipid mobilization is dependent on an acidic pH and the presence of anionic lipids, whereas cholesterol is able to stabilize the liposomes. We also show for the first time that glycosylation of Sap-B is essential to achieve its full lipid-extraction activity. Removal of the carbohydrate moiety of Sap-B reduces its membrane-destabilizing quality. An unglycosylated Sap-B variant, Asn215His, which causes a fatal sphingolipid storage disease, lost the ability to extract membrane lipids at acidic pH in the presence of BMP.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
1742-464X
pubmed:author
pubmed:issnType
Print
pubmed:volume
274
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
3405-20
pubmed:meshHeading
pubmed:year
2007
pubmed:articleTitle
Saposin B mobilizes lipids from cholesterol-poor and bis(monoacylglycero)phosphate-rich membranes at acidic pH. Unglycosylated patient variant saposin B lacks lipid-extraction capacity.
pubmed:affiliation
LIMES, Membrane Biology & Lipid Biochemistry Unit, c/o Kekulé-Institut für Organische Chemie und Biochemie, University of Bonn, Germany.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't