Linked Life Data

10816556

Source:http://linkedlifedata.com/resource/pubmed/id/10816556

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
31
pubmed:dateCreated
2000-9-7
pubmed:abstractText
The lactose transport protein (LacS) of Streptococcus thermophilus belongs to a family of transporters in which putative alpha-helices II and IV have been implicated in cation binding and the coupled transport of the substrate and the cation. Here, the analysis of site-directed mutants shows that a positive and negative charge at positions 64 and 71 in helix II are essential for transport, but not for lactose binding. The conservation of charge/side-chain properties is less critical for Glu-67 and Ile-70 in helix II, and Asp-133 and Lys-139 in helix IV, but these residues are important for the coupled transport of lactose together with a proton. The analysis of second-site suppressor mutants indicates an ion pair exists between helices II and IV, and thus a close approximation of these helices can be made. The second-site suppressor analysis also suggests ion pairing between helix II and the intracellular loops 6-7 and 10-11. Because the C-terminal region of the transmembrane domain, especially helix XI and loop 10-11, is important for substrate binding in this family of proteins, we propose that sugar and proton binding and translocation are performed by the joint action of these regions in the protein. Indeed, substrate protection of maleimide labeling of single cysteine mutants confirms that alpha-helices II and IV are directly interacting or at least conformationally involved in sugar binding and/or translocation. On the basis of new and published data, we reason that the helices II, IV, VII, X, and XI and the intracellular loops 6-7 and 10-11 are in close proximity and form the binding sites and/or the translocation pathway in the transporters of the galactosides-pentosides-hexuronides family.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Aug
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
4
pubmed:volume
275
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
23834-40
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed-meshheading:10816556-Amino Acid Sequence, pubmed-meshheading:10816556-Binding Sites, pubmed-meshheading:10816556-Biological Transport, pubmed-meshheading:10816556-Cysteine, pubmed-meshheading:10816556-Escherichia coli Proteins, pubmed-meshheading:10816556-Ethylmaleimide, pubmed-meshheading:10816556-Lactose, pubmed-meshheading:10816556-Ligands, pubmed-meshheading:10816556-Membrane Transport Proteins, pubmed-meshheading:10816556-Models, Molecular, pubmed-meshheading:10816556-Molecular Sequence Data, pubmed-meshheading:10816556-Monosaccharide Transport Proteins, pubmed-meshheading:10816556-Mutagenesis, Site-Directed, pubmed-meshheading:10816556-Protein Structure, Secondary, pubmed-meshheading:10816556-Protons, pubmed-meshheading:10816556-Sequence Homology, Amino Acid, pubmed-meshheading:10816556-Streptococcus, pubmed-meshheading:10816556-Suppression, Genetic, pubmed-meshheading:10816556-Symporters
pubmed:year
2000
pubmed:articleTitle
Close approximation of putative alpha -helices II, IV, VII, X, and XI in the translocation pathway of the lactose transport protein of Streptococcus thermophilus.
pubmed:affiliation
Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't