Hydrophobics transport across the outer membrane

生物膜形成了细胞与其环境之间的界面，分子通过这一屏障的运输对所有细胞都是必不可少的。尽管人们对亲水性化合物的转运有着丰富的认识，但对疏水分子的膜转运却知之甚少。这是值得注意的，因为生物膜对疏水分子的通过提出了独特的问题。由于脂多糖（LPS）的存在，革兰氏阴性菌的外膜（OM）是防止疏水化合物渗透的特别有效的屏障。唯一被证明可以运输疏水化合物的OM蛋白属于FadL转运蛋白家族。该家族的成员广泛存在于革兰氏阴性菌中，并在长链脂肪酸的摄取中发挥作用

Biological membranes form the interface between cells and their environment, and transport of molecules across this barrier is essential for all cells. Whereas a wealth of knowledge exists about the transport of hydrophilic compounds, very little is known about membrane transport of hydrophobic molecules. This is remarkable, since biological membranes pose unique problems for the passage of hydrophobic molecules. The outer membrane (OM) of gram-negative bacteria is a particularly effective barrier against permeation of hydrophobic compounds, due to the presence of lipopolysaccharide (LPS). The only OM proteins that have been shown to transport hydrophobic compounds belong to the FadL transporter family. Members of this family are widespread in gram-negative bacteria and play a role in the uptake of long-chain fatty acids (LCFAs) and xenobiotics. The goal of this project is to understand in structural and mechanistic terms how such molecules are transported across the OM. More specifically, we will address the following questions: 1. Characterization of FadL-mediated LCFA transport. Using the crystal structures of E. coli FadL as a starting point, we will test and further delineate the proposed model of LCFA transport, by using a combination of site-directed mutagenesis, in vivo transport assays and X-ray crystallography. 2. Characterization of substrate specificity of FadL orthologues involved in LCFA and xenobiotics transport by using in vivo and in vitro substrate binding and transport assays. 3. Mechanism of xenobiotics transport by FadL orthologues. By solving crystal structures of xenobiotics transporters we will determine the structural basis for their substrate specificity. These structures will also allow us to determine whether mechanistic differences exist between LCFA and xenobiotics transport.