Selectivity in solute transport: Binding sites and channel structure in maltoporin and other bacterial sugar transport proteins

BioEssays ◽  
1989 ◽  
Vol 10 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Thomas Ferenci
Keyword(s):  
Solute Transport ◽  
Binding Sites ◽  
Sugar Transport ◽  
Transport Proteins ◽  
Channel Structure

scholarly journals A spin label study of the thyroid hormone-binding sites in human plasma thyroxine transport proteins.

1981 ◽  
Vol 256 (2) ◽  
pp. 831-836
Author(s):  
S.Y. Cheng ◽  
G. Rakhit ◽  
F. Erard ◽  
J. Robbins ◽  
C.F. Chignell
Keyword(s):  
Thyroid Hormone ◽  
Human Plasma ◽  
Spin Label ◽  
Binding Sites ◽  
Transport Proteins ◽  
Hormone Binding ◽  
Label Study

Role of membrane trafficking in plasma membrane solute transport

1994 ◽  
Vol 267 (1) ◽  
pp. C1-C24 ◽  
Author(s):  
N. A. Bradbury ◽  
R. J. Bridges
Keyword(s):  
Plasma Membrane ◽  
Solute Transport ◽  
Membrane Trafficking ◽  
Molecular Mechanisms ◽  
Glucose Transporter ◽  
Water Channel ◽  
Transport Proteins ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Regulated Trafficking

Cells can rapidly and reversibly alter solute transport rates by changing the kinetics of transport proteins resident within the plasma membrane. Most notably, this can be brought about by reversible phosphorylation of the transporter. An additional mechanism for acute regulation of plasma membrane transport rates is by the regulated exocytic insertion of transport proteins from intracellular vesicles into the plasma membrane and their subsequent regulated endocytic retrieval. Over the past few years, the number of transporters undergoing this regulated trafficking has increased dramatically, such that what was once an interesting translocation of a few transporters has now become a widespread modality for regulating plasma membrane solute permeabilities. The aim of this article is to review the models proposed for the regulated trafficking of transport proteins and what lines of evidence should be obtained to document regulated exocytic insertion and endocytic retrieval of transport proteins. We highlight four transporters, the insulin-responsive glucose transporter, the antidiuretic hormone-responsive water channel, the urinary bladder H(+)-ATPase, and the cystic fibrosis transmembrane conductance regulator Cl- channel, and discuss the various approaches taken to document their regulated trafficking. Finally, we discuss areas of uncertainty that remain to be investigated concerning the molecular mechanisms involved in regulating the trafficking of proteins.

scholarly journals Determinants of target prioritization and regulatory hierarchy for the bacterial small RNA SgrS

2017 ◽  
Author(s):  
Maksym Bobrovskyy ◽  
Jane K. Frandsen ◽  
Jichuan Zhang ◽  
Anustup Poddar ◽  
Muhammad S. Azam ◽  
...  
Keyword(s):  
Small Rna ◽  
Binding Sites ◽  
Sugar Transport ◽  
Enteric Bacteria ◽  
Sugar Uptake ◽  
Rna Chaperone ◽  
Target Mrnas ◽  
Mrna Targets ◽  
Molecular Features ◽  
Response To Stress

ABSTRACTThe mechanisms by which small RNA (sRNA) regulators select and prioritize target mRNAs remain poorly understood, but serve to promote efficient responses to environmental cues and stresses. We sought to uncover mechanisms that establish regulatory hierarchy for a model sRNA, SgrS, found in enteric bacteria and produced under conditions of metabolic stress when sugar transport and metabolism are unbalanced. SgrS post-transcriptionally controls a nine-gene regulon to restore growth and homeostasis under stress conditions. An in vivo reporter system was used to quantify SgrS-dependent regulation of target genes and established that SgrS exhibits a clear preference for certain targets, and regulates those targets efficiently even at low SgrS levels. Higher SgrS concentrations are required to regulate other targets. The position of targets in the regulatory hierarchy is not well-correlated with the predicted thermodynamic stability of SgrS-mRNA interactions or the SgrS-mRNA binding affinity as measured in vitro. Detailed analyses of SgrS interaction with asd mRNA demonstrate that SgrS binds cooperatively to two sites and remodels asd mRNA secondary structure. SgrS binding at both sites increases the efficiency of asd mRNA regulation compared to mutants that have only a single SgrS binding site. Our results suggest that sRNA selection of target mRNAs and regulatory hierarchy are influenced by several molecular features. The sRNA-mRNA interaction, including the number and position of sRNA binding sites on the mRNA and cofactors like the RNA chaperone Hfq, seem to tune the efficiency of regulation of specific mRNA targets.IMPORTANCETo survive, bacteria must respond rapidly to stress and simultaneously maintain metabolic homeostasis. The small RNA (sRNA) SgrS mediates the response to stress arising from imbalanced sugar transport and metabolism. To coordinate the stress response, SgrS regulates genes involved in sugar uptake and metabolism. Intrinsic properties of sRNAs such as SgrS allow them to regulate extensive networks of genes. To date, sRNA regulation of targets has largely been studied in the context of “one sRNA-one target”, and little is known about coordination of multi-gene regulons and sRNA regulatory network structure. Here, we explore the molecular basis for regulatory hierarchy in sRNA regulons. Our results reveal a complex interplay of factors that influence the outcome of sRNA regulation. The number and location of sRNA binding sites on mRNA targets and the participation of an RNA chaperone dictate prioritized regulation of targets to promote an efficient response to stress.

scholarly journals Calcium Activation of Ryanodine Receptor Channels—Reconciling RyR Gating Models with Tetrameric Channel Structure

2005 ◽  
Vol 126 (5) ◽  
pp. 515-527 ◽  
Author(s):  
Ivan Zahradník ◽  
Sándor Györke ◽  
Alexandra Zahradníková
Keyword(s):  
Experimental Data ◽  
Binding Sites ◽  
Linear Models ◽  
Experimental Studies ◽  
Calcium Sensitivity ◽  
Channel Structure ◽  
Calcium Dependence ◽  
Calcium Dependent ◽  
Monomer Composition ◽  
The Best Approximation

Despite its importance and abundance of experimental data, the molecular mechanism of RyR2 activation by calcium is poorly understood. Recent experimental studies involving coexpression of wild-type (WT) RyR2 together with a RyR2 mutant deficient in calcium-dependent activation (Li, P., and S.R. Chen. 2001. J. Gen. Physiol. 118:33–44) revealed large variations of calcium sensitivity of the RyR tetramers with their monomer composition. Together with previous results on kinetics of Ca activation (Zahradníková, A., I. Zahradník, I. Györke, and S. Györke. 1999. J. Gen. Physiol. 114:787–798), these data represent benchmarks for construction and testing of RyR models that would reproduce RyR behavior and be structurally realistic as well. Here we present a theoretical study of the effects of RyR monomer substitution by a calcium-insensitive mutant on the calcium dependence of RyR activation. Three published models of tetrameric RyR channels were used either directly or after adaptation to provide allosteric regulation. Additionally, two alternative RyR models with Ca binding sites created jointly by the monomers were developed. The models were modified for description of channels composed of WT and mutant monomers. The parameters of the models were optimized to provide the best approximation of published experimental data. For reproducing the observed calcium dependence of RyR tetramers containing mutant monomers (a) single, independent Ca binding sites on each monomer were preferable to shared binding sites; (b) allosteric models were preferable to linear models; (c) in the WT channel, probability of opening to states containing a Ca2+-free monomer had to be extremely low; and (d) models with fully Ca-bound closed states, additional to those of an Monod-Wyman-Changeaux model, were preferable to models without such states. These results provide support for the concept that RyR activation is possible (albeit vanishingly small in WT channels) in the absence of Ca2+ binding. They also suggest further avenues toward understanding RyR gating.

Treat and trick: common regulation and manipulation of sugar transporters during sink establishment by the plant and the pathogen

2020 ◽  
Vol 71 (14) ◽  
pp. 3930-3940
Author(s):  
Benjamin Pommerrenig ◽  
Christina Müdsam ◽  
Dominik Kischka ◽  
H Ekkehard Neuhaus
Keyword(s):  
Intracellular Transport ◽  
Sugar Transport ◽  
Transport Proteins ◽  
Dependent Manner ◽  
Transport Activity ◽  
Sugar Transporters ◽  
Dependent Processes ◽  
Sink Establishment ◽  
Source And Sink

Abstract Sugar transport proteins are crucial for the coordinated allocation of sugars. In this Expert View we summarize recent key findings of the roles and regulation of sugar transporters in inter- and intracellular transport by focusing on applied approaches, demonstrating how sucrose transporter activity may alter source and sink dynamics and their identities. The plant itself alters its sugar transport activity in a developmentally dependent manner to either establish or load endogenous sinks, for example, during tuber formation and filling. Pathogens represent aberrant sinks that trigger the plant to induce the same processes, resulting in loss of carbon assimilates. We explore common mechanisms of intrinsic, developmentally dependent processes and aberrant, pathogen-induced manipulation of sugar transport. Transporter activity may also be targeted by breeding or genetic modification approaches in crop plants to alter source and sink metabolism upon the overexpression or heterologous expression of these proteins. In addition, we highlight recent progress in the use of sugar analogs to study these processes in vivo.

scholarly journals To be, or not to be two sites: that is the question about LeuT substrate binding

2011 ◽  
Vol 138 (4) ◽  
pp. 467-471 ◽  
Author(s):  
Nicolas Reyes ◽  
Sotiria Tavoulari
Keyword(s):  
Binding Sites ◽  
Journal Club ◽  
Substrate Binding ◽  
Structural Data ◽  
Transport Proteins ◽  
Model System ◽  
Transport Mechanisms ◽  
High Affinity ◽  
The Central Nervous System ◽  
Substrate Binding Sites

Transport proteins of the neurotransmitter sodium symporter (NSS) family regulate the extracellular concentration of several neurotransmitters in the central nervous system. The only member of this family for which atomic-resolution structural data are available is the prokaryotic homologue LeuT. This protein has been used as a model system to study the molecular mechanism of transport of the NSS family. In this Journal Club, we discuss two strikingly different LeuT transport mechanisms: one involving a single high-affinity substrate binding site and one recently proposed alternative involving two high-affinity substrate binding sites that are allosterically coupled.

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