Researchers in Japan have used high-speed atomic force microscopy (AFM) to shoot an action movie of the biological molecular motor ATPase. ATPase, an enzyme embedded in cell membranes, produces the cellular fuel molecule ATP. the enzyme has two rotating components, but until now only X-ray crystallography and similar “still” imaging techniques had been used to visualise how it works. The microscopy work provides more evidence of how changes in conformation of the subunits of the enzyme generate the required rotation to produce ATP.
I covered this scientific discovery for the RSC magazine Chemistry World this week and quoted AFM expert Cindy Berrie of Kansas University. Having asked for her detailed opinion on the work, I thought Sciencebase readers would be interested to see what more she had to say about ATP and AFM.
“This work highlights the power of AFM for structural characterization of proteins, particularly dynamic proteins such as the F1 ATPase molecular motor,” she told me. “The question of how protein molecular motors such as the ATPase function and generate torque is a critically important one, which is still not well understood despite extensive biochemical analysis.” She pointed out that AFM provides a powerful tool to begin to study structure and dynamics in motors such as these and the Japanese work clearly indicates that it is possible to observe structural changes of the ATPase motor proteins using AFM. It has the distinct advantages of working in physiological conditions and without having to add a label to the protein, which might otherwise change the dynamic behaviour of the system.
However, Berrie told me that AFM does have limits in terms of the speed of frame capture and resolution that can be obtained. “In this case, the rotation rate observed for this [ATPase enzyme] ring appears to be slow enough to be captured with this technique. However, the rotation of the native enzyme is much faster, and would likely be much more difficult to observe using this imaging method,” she says. “The observation that conformational changes occur without the presence of the subunit in this ATPase system is interesting and will certainly prompt more investigations of the possibility of cooperativity in the ring itself. If confirmed, this would be nice evidence that the ring itself is involved in the asymmetric nucleotide binding.”
The study does not provide a definitive answer as to whether or not torque is generated in the F1-ATPase motor in this way, but it does provide invaluable new insights.
As to the advent of AFM as a powerful technique in molecular biology, Berrie is rather enthusiastic about its potential. “The relatively recent development of high-speed AFM has allowed dynamics of proteins to be monitored using this technique in addition to the structural information typically obtained from AFM,” she told me. “This technique has been previously used to capture time course of conformation and binding in protein systems including GroEL-GroES and others.” Berrie adds that, “The AFM technique used in this paper has been and will continue to be applied to a variety of protein systems and provides detailed structural data that are difficult to obtain using other techniques. These types of investigations will hopefully ultimately lead to a much better understanding of the mechanism by which these motor proteins function.”
“AFM has clearly gained popularity as a tool for investigation of protein structure and dynamics and with the advent of high speed imaging capabilities, the range dynamical processes which can be studied is increasing. AFM as a tool for imaging biological systems has only been employed for the past decade or so and has made significant advancements and contributions during this time,” Berrie says.
Takayuki Uchihashi, Ryota Iino, Toshio Ando, & Hiroyuki Noji (2011). High-Speed Atomic Force Microscopy Reveals Rotary Catalysis of Rotorless F1-ATPase Science, 333, 755-758