# Presentation: 386786

## Compensatory roles of electrostatics and depletion force on the aggregation of filamentous viruses and protein filaments Jay X. Tang, Brown University,  DMR-0405156 

- Featured Finding: The critical bundling concentration, Cc, decreases exponentially as a function of Bierrum length, lB. This new finding holds for the two divalent counterions tested, Mg 2+ (circles) & Ca 2+ (triangles).
- Ref: Qi Wen & J. X. Tang, Phys Rev Lett, 97: 048101, 2006

- Aggregation of macromolecules is a phenomenon of general interest to physicists, colloidal scientists, and especially biochemists. Numerous proteins and nucleotides form large aggregates under tightly regulated conditions, and thereby perform essential biological functions. The Tang laboratory uses a range of techniques to explore the physical mechanisms of aggregation of bio-macromolecules. Specifically, we use filamentous viruses and protein filaments as test systems, to define the compensatory roles of solution electrostatics and depletion force on their lateral aggregation. Such mechanisms help understand certain cellular and physiological functions in living systems.

## Measuring detachment force of C. cresentus by micromanipulation (Jay X. Tang, Brown University)

-   P. Tsang, G. Li, L. B. Freund, Y. V. Brun & J. X. Tang, PNAS, 103:5764, 2006

- A micromanipulation system has been developed to measure the adhesion of single bacterial cells
- The detachment force varies from 0.11 to 2.26 N (14 cells)
- Average force 0.59+-0.62 N
- Adhesion strength (failure stress) 68 N/mm2 =6800 N/cm2
- Such a strength is stronger than super glue, and is equivalent to
- ~hang 70 tons/(10 cm)2
- ~12 elephants on a palm

## Compensatory roles of electrostatics and depletion force on the aggregation of filamentous viruses and protein filaments Jay X. Tang, Brown University,  DMR-0405156

- Two graduate (Hyeran Kang, female; and Peter Tsang), one undergraduate (Deepa Galaiya, female) and one postdoc (Dr. Guanglai Li) worked on research supported by this  NSF Award.
- The lab web site _[http://biophysics.physics.brown.edu/](http://biophysics.physics.brown.edu/)_
- contains pictures and description of the overall research program, and recent research publications. It is also used in education as the web site of classes taught by Prof. Tang. See, for example,
- _[http://biophysics.physics.brown.edu/ph262.html](http://biophysics.physics.brown.edu/ph262.html)_

**Broader Impact:**
- The project helps to bridge several scientific communities including colloidal physicists and physical chemists, as well as biochemists who share strong interest in protein aggregation and crystallization. Potential applications of the knowledge obtained may help to understand many essential phenomena in various types of soft materials, the studies of which form a growing subfield of condensed matter physics. The program also exemplifies to the general public the importance and benefit of an interdisciplinary approach in modern material science research.

**Compensatory roles of electrostatics and depletion force on the aggregation of filamentous viruses and protein filaments**** **Jay X. Tang, Brown University,  DMR-0405156

## News coverage of a breakthrough report on bacterial adhesion

-  P. Tsang, G. Li, L. B. Freund, Y. V. Brun & J. X. Tang, PNAS, 103:5764, 2006

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**Websites**
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