Crystal structure of the bacterial acetate transporter SatP reveals that it forms a hexameric channel.

Acetate is found ubiquitously in the natural environment and can be used as an exogenous carbon source by bacteria, fungi, and mammalian cells. A representative member of the acetate uptake transporter (AceTr) family named SatP (also yaaH) has been preliminarily identified as a succinate-acetate/proton symporter in Escherichia coli However, the molecular mechanism of acetate uptake by SatP still remains elusive. Here, we report the crystal structure of SatP from E. coli at 2.8 Å resolution, determined with a molecular replacement approach using a previously developed predicted model algorithm, which revealed a hexameric UreI-like channel structure. Structural analysis identified six transmembrane (TM) helices surrounding the central channel pore in each protomer and three conserved hydrophobic residues, FLY, located in the middle of the TM region for pore constriction. According to single-channel conductance recordings, performed with purified SatP reconstituted into lipid bilayer, three conserved polar residues in the TM1 facing to the periplasmic side are closely associated with acetate translocation activity. These analyses provide critical insights into the mechanism of acetate translocation in bacteria and a first glimpse of a structure of an AceTr family transporter.

Crystal structure of monomeric Amuc_1100 from Akkermansia muciniphila.

Many human diseases, such as obesity and diabetes, show annual increases in prevalence and often involve intestinal microbes. One such probiotic bacterium, Akkermansia muciniphila, which was discovered a decade ago, has been reported to influence glucose homeostasis and to contribute to gut health. Amuc_1100, a functionally uncharacterized protein of A. muciniphila, was found to be a key active component in reducing the body weight of mice. Here, the crystal structure of Amuc_1100 (residues 31-317), referred to as Amuc_1100*, is reported at 2.1 Šresolution. Amuc_1100* has a similar fold to three proteins related to pilus formation, PilO, PilN and EpsL, indicating a similar function. Biochemical investigations further confirmed a monomeric state for the soluble region of Amuc_1100, which differs from the dimeric states of PilO, PilN and EpsL. This study provides a structural basis for the elucidation of the molecular mechanism of Amuc_1100.