Apo-intermediate in the transport cycle of lactose permease (LacY).
Proc Natl Acad Sci U S A
; 109(44): E2970-8, 2012 Oct 30.
Article
em En
| MEDLINE
| ID: mdl-23012238
The lactose permease (LacY) catalyzes coupled stoichiometric symport of a galactoside and an H(+). Crystal structures reveal 12, mostly irregular, transmembrane α-helices surrounding a cavity with sugar- and H(+)- binding sites at the apex, which is accessible from the cytoplasm and sealed on the periplasmic side (an inward-facing conformer). An outward-facing model has also been proposed based on biochemical and spectroscopic measurements, as well as the X-ray structure of a related symporter. Converging lines of evidence demonstrate that LacY functions by an alternating access mechanism. Here, we generate a model for an apo-intermediate of LacY based on crystallographic coordinates of LacY and the oligopeptide/H(+) symporter. The model exhibits a conformation with an occluded cavity inaccessible from either side of the membrane. Furthermore, kinetic considerations and double electron-electron resonance measurements suggest that another occluded conformer with bound sugar exists during turnover. An energy profile for symport is also presented.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Proteínas de Membrana Transportadoras
Idioma:
En
Revista:
Proc Natl Acad Sci U S A
Ano de publicação:
2012
Tipo de documento:
Article
País de afiliação:
Estados Unidos
País de publicação:
Estados Unidos