Membrane Transport Group

Jens Preben Morth's research group employs a structural systems biology approach to investigate the proteins involved in acid-base homeostasis and metal ion transport across the cellular membrane.

The kidneys are highly complex organs with the vital role of maintaining homeostasis of small organic solutes and minerals in the body. The proximal tube of the nephron in the kidney absorbs small inorganic solutes from the blood and excretes residual products in the urine, and represents the main site for extensive solute exchange in mammals. It is the solute carrier (SLC) transporters that control this exchange. The exchange of solutes and the regulation of osmotic pressure and acid/base homeostasis in the nephron is of vital importance for animal life.

In ancient Greece, physicians had already noticed small “stones” in the kidneys and the formation of kidney stones is one of the oldest known human disorders. The medical condition is called nephrolithiasis or urolithiasis and is caused by the formation of inorganic crystals usually from calcium, phosphate/oxalate and uric acids (Pak, 1998). A number of diseases have been attributed to the malfunction of anion transporters. Inorganic sulfate is amongst the most abundant anions present in mammalian plasma (Bolt et al, 2004). Sulfate is involved in activating and detoxifying xenobiotics, neurotransmitters, and bile acids. The sulfate ion is essential for the biosynthesis of glycosaminoglycans, cerebroside sulfate and the aminoacids cysteine and methionine. Undersulfation in the cartilage proteoglycans has been associated with human inherited osteochondrodysplasia disorders (Rossi et al, 1996, Thiele et al, 2004). In mammals, the sulfate homeostasis is regulated primarily by the kidney. The majority of sulfate is reabsorbed in the proximal tubules, with only up to 20% is secreted through the urine (Becker et al, 1960).

A project recently started in the Morth group is focused on bicarbonate transporters from the kidney and brain and will benefit from the experience gained over the last several years of working with P-type ATPases. Bicarbonate transporters are involved in the exchange of acids and tightly control the regulation of intracellular pH across the plasma membrane. The system is strongly dependent on the ion gradients maintained by the P-type ATPases. The group aims to develop a complete structural model for anion transport and recognition. The structural analysis of P-type ATPases will also continue with focus on the prokaryotic Ca²⁺-ATPases and Mg²⁺-ATPases, as well as Na⁺/K⁺-ATPase, from both eukaryotic and prokaryotic origin.

Morth’s group also has a keen interest in homology modeling, which is used to link known disease models to structural information. The structural interpretation of both homology models and experimentally determined structures has lead to drug discovery and drug design.

Group Members

Group Leader	Jens Preben Morth
Postdocs	Harmonie Perdreau
	Kim Langmach Hein
PhD Students	Saranya Subramani
	Kaare Bjerregaard-Andersen
	Theis Sommer
Master Students	Jayaram Lamsal
	Sazzad Hossen Toushik
	Nina Fagernes
Principal Engineer	Hanne Guldsten
Photos and contact information for group members.

Methods

A variety of techniques are used in order to identify and characterise both soluble and membrane bound proteins involved in pH regulation. A bioinformatics approach is used to target new proteins and interaction partners of interest. A broad cloning strategy in both eukaryote and bacterial expression systems is employed to search for soluble protein. By developing protocols for the purification and reconstitution of lipid vesicle for membrane proteins, the group is able to study their atomic three-dimensional structure. Structural information is obtained by X-ray crystallography, small angle X-ray scattering (SAXS). Several biophysical and biochemical techniques are also used, including activity assays and isothermal titration calorimetry (ITC) for protein-protein binding and small molecule interactions. The group is currently developing purification and lipid vesicle reconstitution protocols for the membrane proteins to study their three-dimensional atomic structure and aims to purify and characterise members of the SLC4 and SLC26 family.

With these methods, the group hopes to better define both structural models and more functional aspects of acid/base homeostasis. The projects regarding NCBE and NBCn1 are carried out in collaboration with Professor Christian Aalkjaer, Institute of Physiology, Aarhus, Denmark) and Professor Jeppe Praetorius, Institute of Anatomy, Aarhus, Denmark.

• • Becker EL, Heinemann HO Igarashi K, Hodler JE, & Gershberg H (1960) Renal mechanisms for the excretion of inorganic sulfate in man. J Clin Invest 39 : 1909-1913
• • Bolt MJ, Liu W, Qiao G, Kong J, Zheng W, Krausz T, Cs-Szabo G, Sitrin MD, & Li YC (2004) Critical role of vitamin D in sulfate homeostasis: regulation of the sodium-sulfate cotransporter by 1,25-dihydroxyvitamin D3. Am J Physiol Endocrinol Metab 287 : E744-9
• • Pak CY (1998) Kidney stones. Lancet 351 : 1797-1801
• • Rossi A, Bonaventure J, Delezoide AL, Cetta G, & Superti-Furga A (1996) Undersulfation of proteoglycans synthesized by chondrocytes from a patient with achondrogenesis type 1B homozygous for an L483P substitution in the diastrophic dysplasia sulfate transporter. J Biol Chem 271 : 18456-18464
• • Thiele H, Sakano M, Kitagawa H, Sugahara K, Rajab A, Hohne W, Ritter H, Leschik G, Nurnberg P, & Mundlos S (2004) Loss of chondroitin 6-O-sulfotransferase-1 function results in severe human chondrodysplasia with progressive spinal involvement. Proc Natl Acad Sci U S A 101 : 10155-10160

Publications

Selected Publications

1. Laursen M, Bublitz M, Moncoq K, Olesen C, Young H, Moller JV, Nissen P, Morth JP (2009) The structure of sarceplasmic reticulum Ca2+-ATPase bound to cyclopiazonic acid reveals a complexed divalent ion” J Biol Chem. 284,13513-8
2. Morth J. P., Poulsen H., Toustrup-Jensen M. S., Schack V. R., Egebjerg J., Andersen J. P., Vilsen B. & Nissen P. (2009) The structure of the Na+,K+-ATPase and mapping of isoform differences and disease-related mutations. Philos. Trans. R. Soc. Lond. B. Biol. Sci, 364,1514, 217-27
3. Morth J. P., Pedersen B. P., Toustrup-Jensen M. S., Sorensen T. L., Petersen J., Andersen J.P., Vilsen B. & Nissen P. (2007) Crystal structure of the sodium-potassium pump. Nature 450, 1043-1049
4. Morth JP, Gosmann S, Nowak E, & Tucker PA (2005) A novel two-component system found in Mycobacterium tuberculosis. FEBS Lett 579: 4145-4148
5. Morth JP, Feng V, Perry LJ, Svergun DI, & Tucker PA (2004) The crystal and solution structure of a putative transcriptional antiterminator from Mycobacterium tuberculosis. Structure 12: 1595-1605

Full list of Dr. Morth's publications.

 

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