KdpD is a tandem serine histidine kinase that controls K+ pump KdpFABC transcriptionally and post-translationally

Two-component systems, consisting of a histidine kinase and a response regulator, serve signal transduction in bacteria, often regulating transcription in response to environmental stimuli. Here, we identify a tandem serine histidine kinase function for KdpD, previously described as a histidine kinase of the KdpDE two-component system, which controls production of the potassium pump KdpFABC. We show that KdpD additionally mediates an inhibitory serine phosphorylation of KdpFABC at high potassium levels, using not its C-terminal histidine kinase domain but an N-terminal atypical serine kinase domain. Sequence analysis of KdpDs from different species highlights that some KdpDs are much shorter than others. We show that, while Escherichia coli KdpD's atypical serine kinase domain responds directly to potassium levels, a shorter version from Deinococcus geothermalis is controlled by second messenger cyclic di-AMP. Our findings add to the growing functional diversity of sensor kinases while simultaneously expanding the framework for regulatory mechanisms in bacterial potassium homeostasis.

Inhibited KdpFABC transitions into an E1 off-cycle state

KdpFABC is a high-affinity prokaryotic K⁺ uptake system that forms a functional chimera between a channel-like subunit (KdpA) and a P-type ATPase (KdpB). At high K⁺ levels, KdpFABC needs to be inhibited to prevent excessive K⁺ accumulation to the point of toxicity. This is achieved by a phosphorylation of the serine residue in the TGES₁₆₂ motif in the A domain of the pump subunit KdpB (KdpB_S162-P). Here, we explore the structural basis of inhibition by KdpB_S162 phosphorylation by determining the conformational landscape of KdpFABC under inhibiting and non-inhibiting conditions. Under turnover conditions, we identified a new inhibited KdpFABC state that we termed E1P tight, which is not part of the canonical Post-Albers transport cycle of P-type ATPases. It likely represents the biochemically described stalled E1P state adopted by KdpFABC upon KdpB_S162 phosphorylation. The E1P tight state exhibits a compact fold of the three cytoplasmic domains and is likely adopted when the transition from high-energy E1P states to E2P states is unsuccessful. This study represents a structural characterization of a biologically relevant off-cycle state in the P-type ATPase family and supports the emerging discussion of P-type ATPase regulation by such states.

Molecular Mechanisms for Bacterial Potassium Homeostasis

Potassium ion homeostasis is essential for bacterial survival, playing roles in osmoregulation, pH homeostasis, regulation of protein synthesis, enzyme activation, membrane potential adjustment and electrical signaling. To accomplish such diverse physiological tasks, it is not surprising that a single bacterium typically encodes several potassium uptake and release systems. To understand the role each individual protein fulfills and how these proteins work in concert, it is important to identify the molecular details of their function. One needs to understand whether the systems transport ions actively or passively, and what mechanisms or ligands lead to the activation or inactivation of individual systems. Combining mechanistic information with knowledge about the physiology under different stress situations, such as osmostress, pH stress or nutrient limitation, one can identify the task of each system and deduce how they are coordinated with each other. By reviewing the general principles of bacterial membrane physiology and describing the molecular architecture and function of several bacterial K⁺-transporting systems, we aim to provide a framework for microbiologists studying bacterial potassium homeostasis and the many K⁺-translocating systems that are still poorly understood.

Identification of tissue factor in two human pancreatic cancer cell lines

We have studied the effects of two human pancreatic cancer and two human small cell lung cancer cell lines on clotting and platelet aggregation. Both pancreatic lines markedly shortened recalcification times and induced platelet aggregation. The lung cancer lines produced little shortening of recalcification times and no platelet aggregation. The clotting and aggregation activities of the pancreatic lines were further characterized. Recalcification times following the addition of cancer cell line material to plasmas deficient in factors VII and X were markedly prolonged, suggesting that the activity is due to tissue factor. Hirudin, an inhibitor of thrombin from the saliva of leeches, and rabbit polyclonal immunoglobulin G anti-bovine brain tissue factor inhibited both procoagulant and aggregation activities. Apyrase (an enzyme degrading ADP), diisopropylfluorophosphate (a serine protease inhibitor) and L-trans-epoxysuccinylleucylamido(4-guanidino)butane (a cysteine protease inhibitor) failed to inhibit these activities. Increasing concentrations of heparin inhibited platelet aggregation. Subcellular fractionation studies showed these activities to be localized to the plasma membrane. The association between mucin and the acceleration of clotting has been well described. The absence of mucin in electron micrographs of these pancreatic whole cells, membrane fractions, and shed microvesicles, as well as the failure of chaotropic agents (i.e., agents stripping material extrinsic to the cell membrane such as mucin) to abrogate this activity support these activities being intrinsic to the plasma membrane. These data strongly suggest that these activities are due to tissue factor which appears to be released as microvesicles in vitro. The release of tissue factor via microvesicles in vivo is one possible mechanism for the coagulopathy sometimes seen in patients with pancreatic carcinoma.

Hemolytic uremic syndrome in a patient with small cell lung cancer

Hemolytic uremic syndrome is a rare entity in patients with carcinoma and presents with a triad of renal insufficiency, microangiopathic hemolytic anemia, and thrombocytopenia. We report this syndrome for the first time in a patient with small cell lung carcinoma. Spontaneous platelet aggregation of washed normal platelets was demonstrated using patient plasma. Circulating immune complex levels were not elevated. The entity completely resolved after treatment with plasma, vincristine, aspirin, and dipyridamole.

Acute nonlymphocytic leukemia after thiotepa instillation into the bladder: report of 2 cases and review of the literature

We report 2 cases of acute nonlymphocytic leukemia after thiotepa instillation into the bladder for superficial bladder carcinoma and review 4 additional cases from the literature. Intravesical thiotepa is absorbed systemically in patients with bladder carcinoma and such treatment may be associated with the rare occurrence of acute nonlymphocytic leukemia and/or the myelodysplastic syndrome.