Protein-directed self-assembly of a fullerene crystal
Authors: Nam Hyeong Kim
Christopher B Murray
Yong Ho Kim
Gevorg Grigoryan
Shao-Qing Zhang
Kook-Han Kim
Jaydeep Paul
Dong-Kyun Ko
Rudresh Acharya
Yong-Tae Kim
William F DeGrado
Journal: Nature Communications (2016)
Discipline: Multidisciplinary
Keywords: self-assembly; proteins; buckminsterfullerene; superstructures; crystal structure
Affiliations: SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea., Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, USA., School of Biological Sciences, National Institute of Science Education and Research, Bhubaneswar, Odisha 752050, India., Department of Pharmaceutical Chemistry and Cardiovascular Research Institute, University of California, San Francisco, California 94158, USA., Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA., Department of Chemistry and Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA., Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon 16419, Korea., Department of Computer Science and Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.

Abstract:  Learning to engineer self-assembly would enable the precise organization of molecules by design to create matter with tailored properties. Here we demonstrate that proteins can direct the self-assembly of buckminsterfullerene (C60) into ordered superstructures. A previously engineered tetrameric helical bundle binds C60 in solution, rendering it water soluble. Two tetramers associate with one C60, promoting further organization revealed in a 1.67-Å crystal structure. Fullerene groups occupy periodic lattice sites, sandwiched between two Tyr residues from adjacent tetramers. Strikingly, the assembly exhibits high charge conductance, whereas both the protein-alone crystal and amorphous C60 are electrically insulating. The affinity of C60 for its crystal-binding site is estimated to be in the nanomolar range, with lattices of known protein crystals geometrically compatible with incorporating the motif. Taken together, these findings suggest a new means of organizing fullerene molecules into a rich variety of lattices to generate new properties by design. 

Retracted: No

PubPeer comments:
 Supplementary figures 4b and 4c are essentially the same. An error? Authors comment is expected. ![file] , 
 Thank you so much for your question. The difference between supplementary figures 4b and 4c is different fittings for the same set of data: 4b for *single species* and 4c for *double species* (distribution of the two species is shown in figure 4d). The resulting fitting curves are extremely similar, and only the residuals can display the minute difference. , 
 #2 To my eye, I can t see any difference in the residuals; do you have the raw data for the datapoints and the equations of those curves available? , 
 #3 they are noticeably different. look at the bar plots at the very right at the top. there are more red bars in b than c (above the axis). also inspect the blue bars below the red bars (beneath the axis): they have different heights for b and c . the green bars to the right of the said-red bars (above the axis) are also different in b and c . in short: zoom in on the pdf and inspect closer. , 
 So they are similar, you are right. But that s sort of the point. Part b is a single-species fit, which fits fairly well to a molecular weight of about ~7 times the weight of the peptide. Part c is a two-species fit of monomer and octamer, and fits slightly better (but similarly). And, importantly, the dissociation constant that is produced indicates that it would be predominantly octameric at the tested concentration (which then corresponds well to the single-species and two-species fits looking similar). So taken together, and with the SEC results in the paper, suggests that the higher-order (likely octameric) association starts in solution before crystallization, which if I remember correctly was the main point we were driving with this figure. , 
 Also, keep in mind that the  data in these two figures is the same (the data points), and only the fit is different. , 
 #6 Data is the same, I agree (and it should be). #5 You say that the two-species fit is slightly better (albeit very similar to single-species), do you have any numerical  goodness of fit value to compare the two? E.g. MSE, R^2, etc. If this is important to the publication (which I realize it might not be, given that this is in the supplement), it might be useful for readers to have a statement to the effect of  Single species fit has R^2 of 0.98, but two species has a fit of 0.99... #4 Zooming in on the residual (or any part, but I ll use the residual since it s a bit easier to compare), the two plots look almost identical, with the exception that the red bars in C are slightly narrower than in B . Also, all of the blue, black, and green bars look identical. Again, raw data would be helpful. ![file] ,