Escherichia coli membranes depleted of SecYEG elicit SecA-dependent ion-channel activity but lose signal peptide specificity.
J Membr Biol
; 245(11): 747-57, 2012 Nov.
Article
em En
| MEDLINE
| ID: mdl-22854753
ABSTRACT
We have developed a sensitive method to detect the opening of SecA-dependent, protein-conducting channels in Xenopus oocytes. In this study, we determined the ionic current activities of the SecA-dependent channel from membrane vesicles depleted of SecYEG. We found that these SecYEG-depleted membranes produced SecA-dependent ionic currents in the oocytes, as did membranes containing SecYEG. However, reconstituted membranes depleted of SecYEG required higher concentrations of SecA to elicit ionic currents like those in membranes containing SecYEG. In contrast to membranes containing SecYEG, the proofreading capacity of signal peptides was lost for those membranes lacking SecYEG. These findings are consistent with loss of signal peptide specificity in channel activity from membranes of SecY suppressor or SecY plug domain mutants. The signal peptide specificity of the reconstituted membranes, like SecA-liposomes, can be restored by the addition of SecYEG proteoliposomes. On the other hand, the channel activity efficiency of reconstituted membranes was fully restored, while SecA-liposomes could only be partially enhanced by the addition of SecYEG, indicating that, in addition to SecYEG, other membrane proteins contribute to the efficiency of channel activity. The SecA-dependent channels in membranes that lacked SecYEG also lost ion selectivity to monovalent cations but retained selective permeability to large anions. Thus, the electrophysiological evidence presented here indicates that SecYEG is not obligatory for the channel activity of Escherichia coli membranes, as previously shown for protein translocation, and that SecYEG is important for maintenance of the efficiency and specificity of SecA-dependent channels.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Proteínas de Membrana Transportadoras
/
Proteínas de Bactérias
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Sinais Direcionadores de Proteínas
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Membrana Celular
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Adenosina Trifosfatases
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Proteínas de Escherichia coli
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Escherichia coli
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Canais Iônicos
Limite:
Animals
Idioma:
En
Revista:
J Membr Biol
Ano de publicação:
2012
Tipo de documento:
Article
País de afiliação:
Estados Unidos