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An interview with

Arnold Boersma

, a research

fellow at the University of Groningen and co-cor-

responding author on the paper,

A Sensor for Mac-

romolecular Crowding in Living Cells

, A.J. Boersma,

I.S. Zuhorn, and B. Poolman;

Nat Methods

, 2015,

12: 227-229.

Arnold, could you describe the molecular

components of your sensor?

The crowding sensor

consists of three parts, two fluorescent proteins

connected by a flexible linker that includes two

stable helices. The fluorescent proteins form a

FRET pair, allowing one to monitor the size (com-

pactness) of the molecule in response to crowding


What experiment convinced you that the sensor

is responding to changes in excluded volume?

The FRET signal increases with increasing size or

amount of added polymers like Ficoll, but the cor-

responding monomers (


sucrose) do not change

the signal, ruling out direct chemical interactions.

How were the measurements obtained with

living cells?

The intensities of the emission of the

FRET donor and acceptor were determined by

confocal microscopy. Taking into account auto-

fluorescence from the cells, the ratio of the two

fluorophores was determined after splitting the

emission into two channels.

How did you alter the extent of crowding, and

what was the result?

We increased the osmolar-

ity of the medium which leads to dehydration of

the cells and an increase in crowding. When we

tested the sensor under these conditions, we indeed

observed an increase in the FRET signal, which

diminished when we allowed the cells to adapt to

the osmotic stress.

What next?

This research was done as part of a

grant aimed at developing an independent line

of research, hosted in

Bert Poolman’s


Next, I’m planning to continue on this path and

further improve our understanding of the physi-

cochemical environment in the cell – there is still

much to learn about the cell interior which cannot

be extracted from the genome but is crucial for life!

BIV Subgroup Store

Need to commemorate the achievement of a lab

group member or colleague? Consider buying a

unique gift from the BIV Subgroup Store! (http://

Daryl K. Eggers

, Subgroup Secretary-Treasurer

Grants and Opportunities

East Asia and Pacific Summer Institutes for

U.S. Graduate Students (EAPSI)



provide U.S. graduate students in

science, engineering, and education first-hand

research experiences in Australia, China, Japan,

Korea, New Zealand, Singapore, or Taiwan; an

introduction to the science, science policy, and

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and an orientation to the society, culture, and




12, 2015



The Sunnybrook Research Prize


Student should be in third or fourth

year of study at a Canadian university by Fall

2015 and have completed a research project with

a focus on biomedical research.



29, 2015



Arnold Boersma