New instrument at SciLifeLab reduces common cryo-EM problem

The long-term problem in cryo-EM about insufficient data due to uneven protein molecules distribution can now be reduced thanks to a new instrument for specimen preparation of cryo-EM grids, the Chameleon.

Chameleon grid holder. Photo: Matthew Bennett

Chameleon is a sophisticated robotic sample spraying device (see video below), originally developed under the name Spotiton in the group of Bridget Carragher at NYSBC. This next-generation sample preparation machine is meant to alleviate a common problem in cryo-EM known as the air-water-interface problem.

“It has been observed that the majority of protein molecules trapped in a thin film buffer tend to orient in a specific way or unfold and even precipitate at the interface between the air and the liquid, maybe due to microfluidic tension forces”, says Dr. Marta Carroni, from Stockholm University’s Department of Biochemistry and Biophysics at SciLifeLab, Solna. 

“While in many cases we get away with this problem as there are enough folded proteins nicely embedded in the ice, sometimes, and unfortunately quite often, the problem results in incompleteness of the data. What happens is that the molecules organize themselves in a specific way at the air water interface presenting always the same orientation. And, in order to be able to obtain 3-dimensional structures, we need to visualize the proteins in many random orientations”, she continues.

By very rapidly spraying the sample on top of special support grids, at a speed in the range of 50 to 900 msec, the air-water-interface problem can be reduced. 
The robotic device offers a number of possibilities for various projects run at the cryo-EM national Scilifelab facility. After a familiarisation period of three months for the cryo-EM unit personnel and members of Marta’s group, the instrument will be made available to the user community, via personal training courses and/or pure service access. 

“Some are already coming up with requests for alternative usage of the Chameleon, so I hope that there will be some fun method development related to it”, says Dr. Marta Carroni.  

The acquisition of the Chameleon was made possible thanks to funding from the Swedish Foundation for Strategic Research (SSF) and SciLifeLab Campus Solna expensive instrument RED initiative to Dr. Marta Carroni with additional help from Pretzel Therapeutics industrial-user fees.