OccK Channels from Pseudomonas aeruginosa Exhibit Diverse Single-Channel Electrical Signatures but Conserved Anion Selectivity
详细信息 查看全文
- 作者：Jiaming Liu ; Elif Eren ; Jagamya Vijayaraghavan ; Belete R. Cheneke ; Mridhu Indic ; Bert van den Berg ; Liviu Movileanu
- 刊名：Biochemistry
- 出版年：2012
- 出版时间：March 20, 2012
- 年：2012
- 卷：51
- 期：11
- 页码：2319-2330
- 全文大小：577K
- 年卷期：v.51,no.11(March 20, 2012)
- ISSN：1520-4995
文摘
Pseudomonas aeruginosa is a Gram-negative bacterium that utilizes substrate-specific outer membrane (OM) proteins for the uptake of small, water-soluble nutrients employed in the growth and function of the cell. In this paper, we present for the first time a comprehensive single-channel examination of seven members of the OM carboxylate channel K (OccK) subfamily. Recent biochemical, functional, and structural characterization of the OccK proteins revealed their common features, such as a closely related, monomeric, 18-stranded 尾-barrel conformation with a kidney-shaped transmembrane pore and the presence of a basic ladder within the channel lumen. Here, we report that the OccK proteins exhibited fairly distinct unitary conductance values, in a much broader range than previously expected, which includes low (40鈥?00 pS) and medium (100鈥?80 pS) conductance. These proteins showed diverse single-channel dynamics of current gating transitions, revealing one-open substate (OccK3), two-open substate (OccK4鈥揙ccK6), and three-open substate (OccK1, OccK2, and OccK7) kinetics with functionally distinct conformations. Interestingly, we discovered that anion selectivity is a conserved trait among the members of the OccK subfamily, confirming the presence of a net pool of positively charged residues within their central constriction. Moreover, these results are in accord with an increased specificity and selectivity of these protein channels for negatively charged, carboxylate-containing substrates. Our findings might ignite future functional examinations and full atomistic computational studies for unraveling a mechanistic understanding of the passage of small molecules across the lumen of substrate-specific, 尾-barrel OM proteins.