Water Channels2003 Chemistry Nobel

Prize

Kristi McKeeSFASU Fall 2003

Scientific Discovery

Importance of this Award

70% of living systems are made up of water.

Have to have some type of mechanism to move water and important ions around.

Cell Membrane The cell membrane is important in

protecting the cells organelles from the environment and transporting nutrients in and waste out of the cell.

Cell Membrane

The cell membrane is made up of mostly phospholipidis and proteins.

Cell Membrane

Phospholipids have a hydrophilic and hydrophobic ends.

The phosphate head is charged while the carbon tail is not charged.

Phopholipid Structure

Cell Membrane

Three types of predominant proteins in the membrane:Transport ProteinsMarker ProteinsReceptor Proteins

Cell Membrane

Transport Proteins – regulate transport and diffusion across membrane. There are two forms: Carrier Channel

Carrier Proteins

They do not extend the whole distance of membrane, instead move back and forth carrying nutrients and waste in and out.

Channel Proteins

Some act as a passive pore to allow diffusion of water and some other molecules.

Does not require energy.

History

1890 Wilhelm Ostwald proposed the idea that electric signals were produced by ions moving in and out of the cell. He was awarded the Nobel Prize in 1909 for the discovery.

History

John Eccles, Alan Hodgkin and Andrew Huxley were able to show how potassium and sodium ions were involved in chemical cascades (i.e. eyes watering, muscles contracting) They were awarded a Nobel Prize in the 1963.

HIstory

Jens Skou awarded the Nobel Prize in Chemistry in 1997 for discovery of Sodium-Potassium Pumps.

History

In the 1970’s scientists were able to prove that some channels were specific to only particular type of ions.

However, no one had yet been able to see what a water channel actually does, how it looks.

Advance of Science

In the late 1980’s protein science had advanced for the study of molecular machinery of how proteins may work and function.

By 1992 scientists were able to identify which proteins were involved in channels.

Peter Agre

Peter Agre

BA in Chemistry 1970 Augsburg College

MD 1974 from Johns Hopkins University School of Medicine

1974 – 75 Postdoctoral Fellowship Johns Hopkins Dept of Pharamacology

Agre

1975 – 78 Internship and Residency at Case Western Reserve University Dept. of Medicine

1978 – 80 Postdoctoral Fellowship At Univ. of N. Carolina at Chapel Hill Dept. of Medicine Hematology/Oncology Div.

1980 – 81 Clinical Asst. Professor of Medicine Univ. of N. Carolina at Chapel Hill

Agre

1980 – 81 Senior Clinical Research Scientist

1981 – 83 Research Associate Johns Hopkins School of Medicine Dept. of Cell Biology/Anatomy and Medicine

1984 – 93 Asst. Professor Johns Hopkins

1990 – 94 Co-Director Office of Research Planning Dept. of Medicine

Agre

1993 – present Professor Johns Hopkins School of Medicine Departments of Biological Chemistry and Medicine

1996 – 1999 Director of John Hopkins Graduate Program in Cellular and Molecular Medicine (CMM)

1999 – present Chair Advisory Board Johns Hopkins Graduate Program in CCM

Agre’s Work

In mid-1980’s he studied various proteins found in the membrane of red blood cells and also found one in the kidneys and was able to determine the peptide sequence and the corresponding DNA sequence. (CHIP28 28kDa)

Agre’s Work

Expressed the CHIP28 in Xenopus oocytes and placed in hypo-osmotic medium and noticed the cells swelling rapidly.

Agre’s Work

He tested his theory by a simple experiment by comparing two cells one with this protein and one without. When exposed to water the ones with the protein swelled and one without remain unchanged.

Agre’s Work

Agre’s Work

Also ran trials on artificial cells called liposome (type of soap bubble with water on inside and out) Also found the cells with the protein (CHIP28) inserted in membrane acted as previous cells.

He termed these channel proteins aquaporin, “water pore”.

Agre’s Work

From knowledge that Hg+2 blocks water movement in cells he was able to show the cells with the protein were also rendered inactive by the mercury ions. This finding made him believe that his discovery was actually a water channel.

Agre’s Work

In 2000 with other research scientists, he was able to show the first three-dimensional of an aquaporin (Aquaporin-1 from human red blood cell).

Agre’s Work

Phylogenetic Tree

The Other Half

Roderick MacKinnon

Roderick MacKinnon

BS 1978 Brandeis University in Biochemistry

MD 1982 Tufts Medical School in Boston

1985 Completed residency at Beth Israel Hospital, Harvard, board Certified in internal medicine.

MacKinnon

1985 – 86 Postdoctoral Fellowship in Dept of Medicine at Beth Israel Hospital.

1986 – 89 Postdoctoral Fellowship in Dept. of Biochemistry at Brandeis.

1989 – 91 Asst Professor in Dept. of Cellular and Molecular Physiology, Harvard Medical School.

MacKinnon

1991 – 92 Asst. Professor in Dept. of Neurobiology, Harvard Medical School.

1992 received PEW Scholar in Biomedical Sciences and McKnight Scholars Award

1995 Received Biophysical Society Young Investigator Award and was promoted to full Professor at Harvard Medical School Dept. of Neurobiology.

MacKinnon

1996 – Present Professor in Laboratory of Molecular Neurobiology and Biophysics and Rockefeller University, New York City. Also an Investigator at the Howard Hughes Medical Institute.

1999 Awarded Lasker Award for Basic Medical Research on work with ion channels.

MacKinnon

Took a new approach to try and crack the controversy of ion channel proteins.

First worked with scorpion toxin that was discovered to block potassium channels that lead to the discovery of the shaker gene.

MacKinnon

Discovered that potassium channels had to be tetramers by binomial statistics and the toxin experiments.

MacKinnon

Using his skills and the advancements of X-ray crystallography, MacKinnon taught himself the fundamentals and presented the structure of an ion channel in April of 1998 (KcsA from the bacterium Streptomyces lividans).

Also revealed how ion channel functions at an atomic level.

MacKinnon

MacKinnon

Two types of ion channels studied and discovered how they differentiated between ions:Potassium channelsSodium channels

MacKinnon

The channels had a selective “filter” in the P-loop, and a sensor to determine when to let the ions in and out of the cell.

Discovered in the potassium channel that the spacing between the K+ and the oxygen atoms in the filter and the sodium ions do not fit so they remain behind in the water solution.

MacKinnon

MacKinnon

Ion Channel GatingIon channel gating refers to opening and closing of the ion conduction pore in response to a specific stimulus.

Certain channels open when ligands bind (ligand-gated channels); others open in response to membrane voltage (voltage-gated channels).

MacKinnon

Studied diffusion-limited rates by analysis of ion conduction on potassium channels using K+ and Rb+

Used Rb because they are know to penetrate K channels.

Found K+ ion is passed and rehydrated in approximently ten nanoseconds.

Channels

Types of channelsWater – They are responsible to

transportation of water in and out of the cell.

Ion – Move ions in and out to conduct such things as signal cascades.

Aquaglyceroporins – Trasport glycerol and other small molecules across membrane.

Channels

There are now 11 different variants of these channels in the human body and more may still be discovered.

They are responsible for many reactions in the body one major function is done in the kidneys.

Body Functions

170 liters of primary urine produced in 24 hours but only approximently 1 liter is excreted per day.

This is due to the mechanisms in kidneys:70% of water reabsorbed by AQP1

into blood10% of water reabsorbed by AQP2

Kidney Tubules

Diseases related to Ion Channels

Several disease states are related to dysfunctional ion channels. cardiac arrhythmiasdiabeteshypertension angina pectorisepilepsy

Diseases Related to Defects with Ion Channels

Alzheimer’s Disease Parkinson’s Schizophrenia Thought to result from dysfunction of

voltage gated channels

Defects in Ion Channels

1989 cystic fibrosis was first discovered to be as a defect in ion channels.

Epilepsy caused from synchronised bursts in nerve cells in the brain that result in seizures. Disorder was found in the beta subunit or in the alpha subunit in voltage-gated sodium channel. Defect in a single change of amio acid residue.

Defect in Aquaporins

A deficiency in the antidiureti hormone, vasopressin, may be affected by diabetes insipidus and show an increase of urine excretion to 10 – 15 liters a day.

Drug Targeting

Already today, drugs targeting ion channels generates over 6 billion dollars in sales per annum. According to the FDA, the number of new approved drugs targeting ion channels is equal to or even higher than that for drugs targeting proteases, polymerases and reverse transcriptases.

Resources

Agre, Peter; Bonhivers, Melanie; Borgnia, Mario J. “The Aquaporins, Blueprints for Cellular Plumbing Systems,” Jounal of Biological Chemistry Vol. 273, Issue 24. June 12, 1998. pp 14659 – 14662.

“An Interview with Roderick MacKinnon,” Lasker Foundation. www.laskerfoundation.org/awards/library/1999b_int_mr2.shtml.

“Boigraphy of Roderick MacKinnon” Lasker Foundation. www.laskerfoundation.org/awards/library/ 1999b_boi_mr.shtml

Bowen, R. “Aquaporins: Water Channels” www.arbl.cvmbs.colostate.edu/hbooks/molecules/aquaporins.html

Resources

Cell Membrane Cartoon. www.people.virginia.edu/~rjh9u/cellmembrane.html

“Chemistry Channels” Spotlight www.psigate.ac.uk/spotlight/issue13b/chemistry.html

Dworakowska, Beata; Dolowy, Krzysztof. “Ion Channels-related Diseases,” Acta Biochimica Polonica Vol. 47 No. 3, July 27, 2000. pp. 685 – 703.

Hard, Trude. “Potassium Channels in Guard Cells – From Phenomenon to Structural Analysis,” www.iwf.de/iwfeng/3medien/33db/333/c7041.html

Resources

Jensen, Morten O; Tajkhorshid, Emad; Schulten, Klaus. “Electrostatic Tuning of Permeation and Selectivity in Aquaporin Water Channels,” Boiphysical Journal. Vol 85. November 2003. pp 2884 – 2899.

Karow, Julia. “Interview with Roderick MacKinnon,” March 4, 2002. Scientific American. www.sciam.com

Keeley, Jim. “Researchers Discover Structure of Nature’s ‘Circuit Breaker,’” April 30, 2003. www.eurekalert.org/pub_releases/2003-04/hhmi-rds042903.php

Resources

Morals-Cabral, Joao H; Zhou; Yufeng; MacKinnon, Roderick. “Energetic Optimization of Ion Conduction Rate by the K+ Selectivity Filter,” Nature. Vol. 414, November 2001pp. 37 – 42.

Morrill, James A.; MacKinnon, Roderick. “Isolation of a Single Carboxyl-Carboxylate Proton Binding Site in the Pore of a Cyclic Nucleotide-gated Channel,” Journal of General Physiology. Vol. 114 July 1999. pp. 71 – 83.

Resources

Nobel Prize in Chemistry. Advanced Information for Public. www.nobel.se

“Nobel Prize in Chemistry 2003 - Information for the Public” www.nobel.se/chemistry/laureates/2003/public.html

Phospholipid Structure. www.bact.wisc.edu/microtextbook/bacterialstructure/membraneGen.html

“Structure and Mechanism of Ion Channels,” www.hhmi.org/research/investigators/mackinnon.html

Resources

“Shaping better Understanding of Potassium Channels,” www.hhmi.org/news/mackinnon6.html

Structural Studies Reveal How Potassium Channels are Inactivated,” www.hhmi.org/newsmackinnon4.html

The Virtual Cell Web Page Ch 3 Cell Biology. www.personal.tmlp.com/Jimr57/textbook/chapter3.htm

Voltage Dependent Potassium Channel. Roderick MacKinnon, Ion Channels. www.osti.gov/accomplishments/mackinnon.html