Linked Life Data

15748994

Source:http://linkedlifedata.com/resource/pubmed/id/15748994

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
2005-3-7
pubmed:abstractText
The ATP binding cassette (ABC) superfamily consists of dozens of families of transport systems, each of which catalyzes uptake or efflux of a specific type of molecule using ATP hydrolysis to energize transport. While all of the ATP hydrolyzing subunits in the superfamily are homologous, a monophyletic origin of the integral membrane constituents is not established. We have identified a subset of these transmembrane proteins that have a basal unit of four transmembrane alpha-helical segments (TMSs) with a large extracytoplasmic domain between TMSs 1 and 2. These homologues were found to exhibit 4, 8 or 10 putative TMSs per polypeptide chain. The two larger topological types exhibit a 4 TMS repeat element resulting from an internal gene duplication event, and the 10 TMS proteins display an extra two putative TMSs between the two repeat units. Rare intragenic deletions in these homologues gave rise to truncated proteins lacking the extracytoplasmic domain, and some phylogenetic clusters of the 4 TMS membrane proteins (but not the 8 or 10 TMS proteins) are fused N-terminal (never C-terminal) to ATP hydrolyzing domains. Bioinformatic analyses lead to the suggestion that in the larger homologues, the second repeat units are more important for function than the first repeat units. Operon analyses suggest that the 4 TMS proteins form heterodimeric complexes while the 8 and 10 TMS proteins incorporate the equivalent of these complexes into single integral membrane polypeptide chains. Different gene compositions of the operons encoding the 4 versus 8 and 10 TMS homologues suggest that these two structural types of transporters act on different types of substrates and serve dissimilar functions. Significant sequence similarity between the integral membrane constituents of the ABC efflux pumps analyzed here and those of other ABC transporters could not be detected. These studies define the evolutionary pathway taken for the appearance of a subset of ABC transmembrane transport proteins and provide clues regarding their mechanistic and functional characteristics.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Mar
pubmed:issn
0923-2508
pubmed:author
pubmed:issnType
Print
pubmed:volume
156
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
270-7
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2005
pubmed:articleTitle
Topological analysis of integral membrane constituents of prokaryotic ABC efflux systems.
pubmed:affiliation
Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, N.I.H., Extramural