Sialic acid and the surface charge associated with hyperpolarization-activated, inward rectifying channels

Fermini, Bernard; Nathan, Richard D.

doi:10.1007/bf01869385

Cited by 10 publications

(5 citation statements)

References 38 publications

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“…In comparative studies, dimethonium has been found to mimic the effects of Mg2+ on flux through monovalent cation channels if the action of Mg2+ is mediated by a screening effect at the channel pore (e.g. Fermini and Nathan, 1990).…”

Section: Results and Discussion Lnhibitor Effects On K+ Flux Across Tmentioning

confidence: 99%

Characterization of a Chloroplast Inner Envelope K+ Channel

Peters

Berkowitz

1994

Plant Physiol.

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A K+-conducting protein of the chloroplast inner envelope was characterized as a K+ channel. Studies of this transport protein in the native membrane documented its sensitivity to K+ channel blockers. Further studies of native membranes demonstrated a sensitivity of K+ conductance to divalent cations such as MgZ+, which modulate ion conduction through interaction with negative surface charges on the inner-envelope membrane. Purified chloroplast inner-envelope vesicles were fused into an artificial planar lipid bilayer to facilitate recording of single-channel K+ currents. These single-channel K+ currents had a slope conductance of 160 picosiemens. Antibodies generated against the conserved amino acid sequence that serves as a selectivity filter in the pore of K+ channels immunoreacted with a 62-kD polypeptide derived from the chloroplast inner envelope. This polypeptide was fractionated using density gradient centrifugation. Comigration of this immunoreactive polypeptide and K+ channel activity in sucrose density gradients further suggested that this polypeptide is the protein facilitating K+ conductance across the chloroplast inner envelope.Studies with intact chloroplasts (Wu and Berkowitz, 1992) indicate that K+ flux across the inner envelope occurs through a well-regulated transport pathway that is likely a K+-conducting ion channel. K' flux into or out of the chloroplast stroma is indirectly linked to H+ counterexchange (Maury et al., 1981; Wu and Berkowitz, 1992). Movement of K+ through this channel protein, therefore, has a profound effect on stromal pH and, hence, photosynthesis (Werdan et al., 1975;Maury et al., 1981; Wu and Berkowitz, 1992). Previous work from this laboratory has demonstrated that a K'-conducting protein can be successfully detergent-solubilized from preparations of purified inner-envelope membrane vesicles and functionally reconstituted into artificial liposomes (Wang et al., 1993). This putative K+ channel protein has not previously been characterized. In the work reported here, we used severa1 approaches to characterize the nature of this K+ transport protein. Results of these experiments are consistent with the presence of a K+ channel in the inner envelope that shares some structural, functional, and regulatory properties with K' channels from other membrane systems ( e g Rudy et al., 1991; Anderson et al., 1992). 955 MATERIALS AND METHODS Preparation of Chloroplast Inner-Envelope Membrane VesiclesInner-envelope vesicles were prepared from spinach (Spinacia oleracea L.) as described previously (Berkowitz and Peters, 1993). Briefly, intact chloroplasts (isolated from 5-10 kg of spinach leaves using Perco11 step gradients) were exposed to freeze/thaw cycles in hyperosmotic medium, and the thylakoids were removed before the crude membrane fraction was loaded on a discontinuous SUC step gradient. Inner-envelope vesicles were removed from the 0.8 ~/ 0 . 4 6 M Suc interface of the gradient, washed in envelope medium (0.2 M SUC, 2 mM Na2EDTA, 2 mM DTT, and 10 m~ TricineNaOH, pH 7.5), a...

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Section: Results and Discussion Lnhibitor Effects On K+ Flux Across Tmentioning

confidence: 99%

Characterization of a Chloroplast Inner Envelope K+ Channel

Peters

Berkowitz

1994

Plant Physiol.

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“…If Mg2+ restriction of K+ influx was due only to screening at a K+ channel pore, dimethonium should mimic the effect of Mg2>. Experimental evidence has supported this assertion; dimethonium has been found to mimic the effects of divalent cations and alter currents through certain types of K+ channels when the action of the divalent cation was attributed to negative surface charge screening (5). With other membrane systems, dimethonium was found not to duplicate the effects of divalent cations, which were predicted to bind to negative charges on the membrane surface (1).…”

Section: Mg2' Treatmentsmentioning

confidence: 57%

“…This procedure allowed for an increase in chloroplast envelope-bound Mg+ (as assayed using both 28Mg2+ and chlorotetracycline fluorescence; 21) and yet also facilitated the quantitative removal of the chloroplasts from solutions containing high levels of free Mg+. For experiments involving this "Mg2+ wash" treatment, control chloroplasts were "washed" by incubation in standard grind medium at 0 to 2°C for 5 Figure 2. High envelope Mg2`did reduce stromal K+ concentration (Fig.…”

Section: Mg2' Treatmentsmentioning

confidence: 99%

Surface Charge-Mediated Effects of Mg²⁺ on K⁺ Flux across the Chloroplast Envelope Are Associated with Regulation of Stromal pH and Photosynthesis

Wu¹,

Peters²,

Berkowitz³

1991

Plant Physiol.

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Studies of Spinacia oleracea L. were undertaken to characterize further how Mg2`external to the isolated intact chloroplast interacts with stromal K+, pH, and photosynthetic capacity. Data presented in this report were consistent with the previously developed that Mg" impairment of stromal alkalization is likely the result of altered H+ fluxes across the chloroplast envelope; altered H+ pumping across the thylakoid membrane is thought not to be involved.Mg2+ effects on H+ movement across the chloroplast envelope are known to be linked to K+ counterflux (2,11,14). However, the specific molecular mechanisms that facilitate fluxes of those monovalent cations and allow for Mg2> regulation of the system are not well characterized. Work from this laboratory (21) has established that it is not Mg2+ external to the chloroplast but rather Mg> bound or associated with the chloroplast envelope that exerts the regulatory effect. It is also clear from several different lines of evidence ( 19, 21 ) that millimolar levels of free external Mg> can greatly affect chloroplast metabolism even though Mg2+ movement across the envelope into the stroma does not occur under these conditions.Two hypotheses have been presented in the literature regarding the specific mechanisms that allow for Mg2+ regulation of H+/K+ counterfluxes. The results of work by Huber and Maury ( 11) and Maury et al. (14) suggest that H+ and K+ movement across the chloroplast envelope both occur via a specific antiport enzyme. They postulated that this transport protein, when activated, can facilitate either K+ influx/H+ efflux or K+ efflux directly linked to H+ influx. These researchers speculated that Mg2+ external to chloroplast activates this antiport enzyme and impairs stromal alkalization in the presence of low external K+ due to net K+ efflux from the stroma (coupled directly to H+ influx). Demmig and Gimmler (2,3) speculated that other mechanisms facilitate K+ and H+ fluxes across the envelope and that Mg2+ may influence this system in a different manner. They proposed that a Donnan system (fixed negative charges) develops in the stroma ofthe illuminated chloroplast, increasing the Em2 (inside negative) between the stroma and extrachloroplast medium. They concluded that this Donnan systemgenerated Em drives monovalent cation influx. At high external K+, influx of K+ occurs. At low external K+, impaired stromal alkalization was thought to occur due to H+ influx. Mg2+ was thought to influence this system by altering external solution ionic strength; the Em was proposed to be dependent on ionic strength of the medium. This model, however, does 2 Abbreviations: Em, membrane potential; dimethonium, ethane-1,2-bis-trimethylammonium; TPP, tetraphenylphosphonium.

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“…These groups can bind to the positively charged regions of P-selectin as anionic polymeric carbohydrate inhibitors . Although the sialic acid groups were also negatively charged, the results of this study indicated that mixed-acid oligosaccharides showed a greater reduction in adhesion to neutrophils than the pure sialylated tetrasaccharide DSLNT . These results suggested that the process of binding to P-selectin was determined by whether the length of the carbon backbone was long enough to reach equilibrium with its charge strength.…”

Section: Structure–function Relationships Of Hmosmentioning

confidence: 71%

Current Advances in Structure–Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

Wang

Chen

Wang

et al. 2022

J. Agric. Food Chem.

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HMOs (human milk oligosaccharides) are the third most important nutrient in breast milk. As complex glycans, HMOs play an important role in regulating neonatal intestinal immunity, resisting viral and bacterial infections, displaying antiinflammatory characteristics, and promoting brain development. Although there have been some previous reports of HMOs, a detailed literature review summarizing the structure−activity relationships and dose-dependent effects of HMOs is lacking. Hence, after introducing the structures and synthetic pathways of HMOs, this review summarizes and categorizes identified structure− function relationships of HMOs. Differential mechanisms of different structural HMOs utilization by microorganisms are summarized. This review also emphasizes the recent advances in the interactions between different health benefits and the variance of dosage effect based on in vitro cell tests, animal experiments, and human intervention studies. The potential relationships between the chemical structure, the dosage selection, and the physiological properties of HMOs as functional foods are vital for further understanding of HMOs and their future applications.

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Sialic acid and the surface charge associated with hyperpolarization-activated, inward rectifying channels

Cited by 10 publications

References 38 publications

Characterization of a Chloroplast Inner Envelope K+ Channel

Characterization of a Chloroplast Inner Envelope K+ Channel

Surface Charge-Mediated Effects of Mg²⁺ on K⁺ Flux across the Chloroplast Envelope Are Associated with Regulation of Stromal pH and Photosynthesis

Current Advances in Structure–Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

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Sialic acid and the surface charge associated with hyperpolarization-activated, inward rectifying channels

Cited by 10 publications

References 38 publications

Characterization of a Chloroplast Inner Envelope K+ Channel

Characterization of a Chloroplast Inner Envelope K+ Channel

Surface Charge-Mediated Effects of Mg2+ on K+ Flux across the Chloroplast Envelope Are Associated with Regulation of Stromal pH and Photosynthesis

Current Advances in Structure–Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

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Surface Charge-Mediated Effects of Mg²⁺ on K⁺ Flux across the Chloroplast Envelope Are Associated with Regulation of Stromal pH and Photosynthesis