The Arabidopsis hyperpolarization-activated (inward-rectifying) K+ channel KAT1 is structurally more similar to animal depolarization-activated (outward-rectifying) K+ channels than to animal hyperpolarization-activated K+ channels. To gain insight into the structural basis for the opposite voltage dependences of plant inward-rectifying and animal outward-rectifying K+ channels, we constructed recombinant chimeric channels between the hyperpolarization-activated K+ channel KAT1 and a Xenopus depolarization-activated K+ channel. We report here that two of the chimeric constructs, which contain the first third of the KAT1 sequence, including the first four membrane-spanning segments (S1-S4) and the linker sequence between the fourth and fifth membrane-spanning segments, express functional channels that retain activation by hyperpolarization, but not depolarization. These two chimeric channels are no longer selective for K+. The chimeras are selective for cations over anions and are permeable to Ca2+. Therefore, unlike animal hyperpolarization-activated K+ channels, in which the carboxyl terminus is important for inward rectification induced by Mg2+ and polyamine block, the plant KAT1 channel has its major determinants for inward rectification in the amino-terminal region, which ends at the end of the S4-S5 linker.

Background & Aims-Increased inflammatory cytokine levels and intestinal epithelial cell apoptosis leading to disruption of epithelial integrity are major pathologic factors in inflammatory bowel diseases. The probiotic bacterium Lactobacillus rhamnosus GG (LGG) and factors recovered from LGG broth culture supernatant (LGG-s) prevent cytokine-induced apoptosis in human and mouse intestinal epithelial cells by regulating signaling pathways. Here, we purify and characterize 2 secreted LGG proteins that regulate intestinal epithelial cell antiapoptotic and proliferation responses.

Bacterial protein toxins alter eukaryotic cellular processes and enable bacteria to successfully colonize their hosts. In recent years, there has been increased recognition that many bacterial toxins are multifunctional proteins that can have pleiotropic effects on mammalian cells and tissues. In this review, we examine a multifunctional toxin (VacA) that is produced by the bacterium Helicobacter pylori. The actions of H. pylori VacA represent a paradigm for how bacterial secreted toxins contribute to colonization and virulence in multiple ways.

Helicobacter pylori is highly adapted for colonization of the human stomach and is present in about half of the human population. When present, H. pylori is usually the numerically dominant gastric microorganism. H. pylori typically does not cause any adverse effects, but is associated with an increased risk of non-cardia gastric adenocarcinoma, gastric lymphoma and peptic ulcer. Disorders such as esophageal diseases and childhood-onset asthma have been recently reported to occur more frequently in individuals who lack H. pylori, compared with H. pylori-positive persons. In this review, we discuss biologic factors that allow H. pylori to colonize the human stomach, mechanisms by which H. pylori increases the risk for peptic ulcer disease and non-cardia gastric adenocarcinoma, and potential benefits that H. pylori might confer to humans.