Department News
Ionic Motion in Biopolymers: Use of Statistics to Model Transport
Seminar Date
2004-04-21
Author
임아주
Date
2004-04-21
Views
1746
1. 제 목
Ionic Motion in Biopolymers: Use of Statistics to Model Transport
and Mechanical Properties of Intracellular Networks
2. 연 사 : Professor A.M. Sastry
Department of Mechanical Engineering / Department
of Biomedical Engineering University of Michigan
3. 일 시 : 2004년 5월 4일 화요일 오후 4시
4. 장 소 : 301동 117호
5. ABSTRACT
If one could be shrunk so as to sit astride a single, fine, filamentary protein in the relatively vast, yet intricate and locally specialized cytoskeletal structure supporting a cell, the heterogeneity within the cytosol, and the stochastic nature of interactions of proteins and ions would be self-evident. The rapidly changing trajectories of signaling ions (e.g. Ca2+, K+, Na+) in the cell might appear (assuming that one’s vision allowed processing of distinct events at the microsecond scale) alternately as Brownian flashes zinging madly among membranes and into and out of organelles, or even as organized clusters of ions into “blips” or “puffs,” or waves, using terms commonly used to describe calcium transport.
Viewing ion transport is not so simple for creatures of order 1m in scale, rather than 1nm, however. Practical experimental markers for microscopic visualization of ions moving in cells requires two basic elements: first, a molecule, generally a protein of many times the atomic mass of the ion, must be found to bind the ion, and second, a means of imaging that molecule in its bound configuration must be found. For the second requirement, use of fluorescent end-groups is a common approach, and sensors for ion transport in wide use, range from free dyes to discrete, bioinert nanoprobes. Following very early work (1881-1887) by the British physiologist Sidney Ringer, who demonstrated conclusively that certain salts were essential for the proper performance of the isolated perfused frog heart: calcium (Ca2+), potassium (K+) and sodium (Na+), generations of workers have successively improved means of targeted, ionic imaging.
The complexity of the environment in which these key ions move cannot be dismissed, given the order-of-magnitude differences between ordinary diffusive and vectorial transport rates. Indeed, modern biology recognizes the cytoskeleton as an intracellular highway system, teeming with signaling ions that zip from site to site along filaments. These tiny particles alternately embrace and slip free of protein receptors with wide-ranging affinities, as they propagate in a blur of motion along cytoskeletal corridors at transport rates far exceeding ordinary diffusive motion. Recent experimental breakthroughs have enabled optical tracking of these single ion binding events in the physiological and diseased states. However, traditional continuum modeling methods have proven ineffective for modeling migration of biometals such as copper and zinc, whose cytosolic concentrations are putatively vanishingly small, or very tightly controlled. Rather, the key modeling problem that must be solved for biometals is determination of the optimal placement of biosensors that bind and detect the metal ions within the heterogeneous environment of the cell. We discuss herein how percolation concepts, in combination with atomistic simulation and sensor delivery models, have been used to gain insights on this problem, and a roadmap for future breakthroughs.
6. 문 의 : 기계항공공학부 민경덕 교수
(☏880-1661)
Ionic Motion in Biopolymers: Use of Statistics to Model Transport
and Mechanical Properties of Intracellular Networks
2. 연 사 : Professor A.M. Sastry
Department of Mechanical Engineering / Department
of Biomedical Engineering University of Michigan
3. 일 시 : 2004년 5월 4일 화요일 오후 4시
4. 장 소 : 301동 117호
5. ABSTRACT
If one could be shrunk so as to sit astride a single, fine, filamentary protein in the relatively vast, yet intricate and locally specialized cytoskeletal structure supporting a cell, the heterogeneity within the cytosol, and the stochastic nature of interactions of proteins and ions would be self-evident. The rapidly changing trajectories of signaling ions (e.g. Ca2+, K+, Na+) in the cell might appear (assuming that one’s vision allowed processing of distinct events at the microsecond scale) alternately as Brownian flashes zinging madly among membranes and into and out of organelles, or even as organized clusters of ions into “blips” or “puffs,” or waves, using terms commonly used to describe calcium transport.
Viewing ion transport is not so simple for creatures of order 1m in scale, rather than 1nm, however. Practical experimental markers for microscopic visualization of ions moving in cells requires two basic elements: first, a molecule, generally a protein of many times the atomic mass of the ion, must be found to bind the ion, and second, a means of imaging that molecule in its bound configuration must be found. For the second requirement, use of fluorescent end-groups is a common approach, and sensors for ion transport in wide use, range from free dyes to discrete, bioinert nanoprobes. Following very early work (1881-1887) by the British physiologist Sidney Ringer, who demonstrated conclusively that certain salts were essential for the proper performance of the isolated perfused frog heart: calcium (Ca2+), potassium (K+) and sodium (Na+), generations of workers have successively improved means of targeted, ionic imaging.
The complexity of the environment in which these key ions move cannot be dismissed, given the order-of-magnitude differences between ordinary diffusive and vectorial transport rates. Indeed, modern biology recognizes the cytoskeleton as an intracellular highway system, teeming with signaling ions that zip from site to site along filaments. These tiny particles alternately embrace and slip free of protein receptors with wide-ranging affinities, as they propagate in a blur of motion along cytoskeletal corridors at transport rates far exceeding ordinary diffusive motion. Recent experimental breakthroughs have enabled optical tracking of these single ion binding events in the physiological and diseased states. However, traditional continuum modeling methods have proven ineffective for modeling migration of biometals such as copper and zinc, whose cytosolic concentrations are putatively vanishingly small, or very tightly controlled. Rather, the key modeling problem that must be solved for biometals is determination of the optimal placement of biosensors that bind and detect the metal ions within the heterogeneous environment of the cell. We discuss herein how percolation concepts, in combination with atomistic simulation and sensor delivery models, have been used to gain insights on this problem, and a roadmap for future breakthroughs.
6. 문 의 : 기계항공공학부 민경덕 교수
(☏880-1661)
