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MIPs and Their Roles in the Exchange of Metalloids

:	Thomas P. Jahn, Gerd P. Bienert
:	Thomas P. Jahn, Gerd P. Bienert
:	MIPs and Their Roles in the Exchange of Metalloids
:	Springer-Verlag
:	9781441963154
:	Advances in Experimental Medicine and Biology
:	1
:	CHF 135.30
:

:	Nichtklinische Fächer
:	English

:	146
:	Wasserzeichen
:	PC/MAC/eReader/Tablet
:	PDF

Sixteen years have passed since human aquaporin-1 (AQP1) was discovered as the first water channel, facilitating trans-membrane water fluxes. Subsequent years of research showed that the water channel AQP1 was only the tip of an iceberg; the iceberg itself being the ubiquitous super family of membrane intrinsic proteins (MIPs) that facilitate trans-membrane transport of water and an increasing number of small, water-soluble and uncharged compounds. Here we introduce you to the superfamily of MIPs and provide a summary about our gradually refined understanding of the phylogenetic relationship of its members. This volume is dedicated to the metalloids, a recently discovered group of substrates for a number of specific MIPs in a diverse spectrum of organisms. Particular focus is given to the essential boron, the beneficial silicon and the highly toxic arsenic. The respective MIP isoforms that facilitate the transport of these metalloids include members from several clades of the phylogenetic tree, suggesting that metalloid transport is an ancient function within this family of channel proteins. Among all the various substrates that have been shown to be transported by MIPs, metalloids take an outstanding position. While water transport seems to be a common function of many MIPs, single isoforms in plants have been identified as being crucially important for the uptake of boric acid as well as silicic acid. Here, the function seems not to be redundant, as mutations in those genes render plants deficient in boron and silicon, respectively.

Thomas P. Jahn is an Associate Professor and group leader at the Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen. He studied biology at the University of Bonn, Germany. From early on in his scientific career he was interested in transport processes in plants and the molecular mechanisms behind these processes. More recently his group contributed to the field of aquaporin research culminating in the identification of several new substrates for members of this superfamily of channel proteins. The overall scope of his current research focuses on the elucidation of networks comprising molecular components engaged in the responses to nutritional stresses, including elements of transport, assimilation, storage and stress signaling. Gerd P. Bienert is currently a Marie Curie Fellow at the Institute of Life Science at the Université Catholique de Louvain in Louvain la Neuve, Belgium. His work focuses on the molecular characterisation of the intracellular trafficking and hetero-oligomerisation of aquaporins in plants. In 2008, he received his PhD in Molecular Plant Nutrition from the University of Copenhagen, Denmark. During his PhD, Gerd Patrick Bienert made significant advances in the scientific understanding on the substrate selectivity of plant aquaporins for uncharged solutes. The work resulted in the molecular identification of the first arsenite, antimonite and hydrogen peroxide channels in plants. Gerd P. Bienert studied biology at the Julius-Maximilians-University Würzburg and at the Technical University Darmstadt, Germany. During his education he emphasized molecular plant physiology and biophysics, genetics and biotechnology. His main research interests focus on the molecular transmembrane transport processes involved in the uptake, translocation and extrusion of compounds that are relevant for plant physiology. In addition, intracellular regulation and trafficking of the transport proteins themselves are also contemplated. In his home region, Tauber-Franken, he began to develop his enthusiastic curiosity for biology by exploring and studying nature. He became fascinated by insects, especially the members of the order of hymenoptera to which he still devotes his free-time. The existing overlap between entomology and botany has aroused his interest in understanding the physiology of plants.

	Title Page	3
	Copyright Page	4
	PREFACE	5
	ABOUT THE EDITORS...	7
	ABOUT THE EDITORS...	8
	PARTICIPANTS	9
	Table of Contents	11
	Chapter 1 Aquaporins: A Family of Highly Regulated Multifunctional Channels	15
	Introduction The Discovery of Aquaporins	15
	Topology of Aquaporins	17
	Selectivity of Aquaporins	17
	Measurement of Aquaporin Activity and Water Movement	18
	Cell Swelling Assays	18
	Stopped-Flow Spectrophotometry	19
	Cell Pressure Probe Measurements	19
	Proton NMR	20
	Aquaporin Inhibition	20
	Phenotype Analysis Reveals Involvement of Aquaporins in Key Physiological Processes	20
	Aquaporin Regulation: Gating and Localization	21
	Phosphorylation	22
	pH and Divalent Cations	23
	Hetero-Oligomerization	24
	Modification of the Subcellular Localization	24
	Conclusion	25
	References	25
	Chapter 2 Phylogeny of Major Intrinsic Proteins	33
	Introduction	33
	A Historical Account of the MIP Phylogeny	33
	Plant MIPs	35
	Phylogenetic Analysis of NIPs	38
	Solute Transport	40
	NIP-Like Bacterial MIPs and Ancestral State of ar/R Filter	40
	Conclusion	41
	References	41
	Chapter 3 Metalloids, Soil Chemistry and the Environment	47
	Introduction	47
	Historical Perspective	48
	Environmental Relevance	49
	Environmental Toxicity of Metalloids	49
	Factors Controlling Bioavailability	50
	Solid: Solution Partitioning of Metalloids	50
	Speciation of Metalloids in the Environment	51
	Assessing Soil Bioavailability of Metalloids	54
	Conclusion	55
	References	56
	Chapter 4 Arsenic Transport in Prokaryotes and Eukaryotic Microbes	60
	Introduction	60
	Metalloid Transport in Prokaryotes	60
	Metalloid Transport in Eukaryotic Microbes	64
	Metalloid Uptake in Yeast	64
	Metalloid Efflux in Yeast	64
	Metalloid Transport in Parasites	65
	Conclusion	66
	References	66
	Chapter 5 Metalloid Transport by Aquaglyceroporins: Consequences in the Treatment of Human Diseases	70
	Introduction	70
	Metalloids and Cancer	72
	Uptake of Metalloids via Human Aquaglyceroporins	72
	Metalloids in Protozoan Parasitic Infections	73
	Parasite Aquaglyceroporins Facilitate Metalloid Transport	74
	Therapeutic Modulation of AQP Permeability	76
	Conclusion	79
	References	79
	Chapter 6 Roles of Vertebrate Aquaglyceroporins in Arsenic Transport and Detoxification	84
	Introduction	84
	Expression of Vertebrate Aquaglyceroporins	84
	Arsenic Is Both an Environmental Toxin and Human Carcinogen	86
	Uptake of Organic and Inorganic Arsenic via Aquaglyceroporins	87
	Molecular Mechanisms for Arsenic Translocation by Aquaglyceroporins	90
	Arsenic Toxicity in Relation of Aquaglyceroporins Regulation	91
	Perspectives	92
	Conclusion	92
	References	92
	Chapter 7 Molecular Mechanisms of Boron Transport in Plants: Involvement of Arabidopsis NIP5	1 and NIP61
	Essentiality of Boron in Plants	96
	Rhamnogalacturonan-II Binds Boron	97
	Involvement of Rhamnogalacturonan-II in B Function	98
	Roles of B Other Than Binding to RG-II	99
	Physiological Analysis of B Transport	99
	Passive Diffusion	99
	Channel-Mediated B Transport	100
	Active B Transport against Concentration Gradients	100
	Molecular Mechanisms of B Transport	101
	BOR1, a Transport Protein Responsible for Xylem Loading	101
	B-Deficiency Sensitive Mutant of Arabidopsis thaliana, bor1-1	101
	B Transport Properties of bor1-1	101
	BOR1 is an Efflux Transporter of Boron	101
	BOR1 Degradation via Endocytosis in Response to High B Supply	102
	BOR1 Paralogs in A. thaliana	103
	A. thaliana NIP5	1, a Channel for Boric Acid Mediates B Uptake under B Limitation103
	Complementary Roles of BOR1 and NIP5	1 in Efficient B Transport under BLimitation104
	NIP6	1, a Channel for Boric Acid Responsible for B Distribution to Leaves under B