C O M P L E X S Y S T E M S A N D B I O M E D I C A L S C I E N C E S

S C I E N T I F I C H I G H L I G H T S

6 6 H I G H L I G H T S 2 0 2 1 I

PRINCIPAL PUBLICATION AND AUTHORS

Hierarchical Assembly Pathways of Spermine-Induced Tubulin Conical-Spiral Architectures, R. Dharan (a,b), A. Shemesh (a,c), A. Millgram (a,c), R. Zalk (d), G.A. Frank (d,e), Y. Levi-Kalisman (c,f), I. Ringel (b), U. Raviv (a,c), ACS Nano 15, 5, 8836-8847 (2021); https:/doi.org/10.1021/acsnano.1c01374 (a) Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem (Israel) (b) Institute for Drug Research, The School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem (Israel) (c) The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem (Israel) (d) The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva (Israel) (e) Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva (Israel) (f) Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem (Israel)

This work was supported by the European Union s Horizon 2020 Research and Innovation programme [grant agreements 736299 and 951943].

REFERENCES

[1] M.A. Ojeda-Lopez et al., Nat. Mater. 13, 195-203 (2014). [2] J. Lee et al., Small 16, 2001240 (2020). [3] A. Shemesh et al., Biochemistry 57, 6153-6165 (2018). [4] F. Madeo et al., Science 359, eaan2788 (2018).

Real-time multi-scale monitoring and tailoring of graphene growth on liquid copper

Complementary in-situ methods of synchrotron X-ray diffraction, Raman spectroscopy and optical microscopy have been used to monitor graphene chemical vapour deposition on liquid copper (at 1370 K at atmospheric pressure conditions), enabling the control of graphene growth at multi-scale, including atomic structure, flake shape, and flake supra-organisation.

Reproducible mass production of large, defect-free two- dimensional materials (2DMs) such as graphene is a major

challenge. Currently, the state-of-the-art method for graphene production is chemical vapour deposition (CVD) on solid copper at elevated temperatures (~1270 K) [1]. As the nucleation of graphene happens at random places on the copper surface (often on defects such as grain boundaries, dislocations, roughness, etc.), this method results in an imperfect multi-domain layer, with domain sizes in the order of micrometres.

Recently, liquid metal catalysts (LMCats) such as molten copper have been employed for the fast growth of uniform hexagonal graphene and other 2DMs of significantly higher quality [2]. The quality of the 2DM is less affected by the catalyst surface structure as it grows on an atomically flat isotropic melt. Efforts have been made

The effect of spermine concentration on tubulin assembly was investigated by mixing 4 mg/ml tubulin with increasing spermine concentrations (between 1 and 20 mM). Using small angle X-ray scattering (SAXS) at beamline ID02 and cryo-electron microscopy (cryo- EM), it was shown that in the presence of spermine, tubulin can assemble into conical-spiral shapes, a very rare structure of materials. The flexibility of tubulin self-association and the interactions between conical spirals facilitated the assembly into complex hierarchical structures (Figure 50). With progressive increase of spermine concentration, tubulin-dimers assembled into conical frustum spirals of increasing length, containing up to three helical turns (Figure 50a,b,d,e). The subunits with three helical turns were then assembled into tubules through base-to-top packing, and formed antiparallel bundles of tubulin conical-spiral tubules in a distorted hexagonal symmetry (Figure 50b,e). Further increase of the spermine concentration led to inverted tubulin tubules assembled in hexagonal bundles (Figure 50c,f).

Time-resolved experiments revealed that tubulin assemblies formed at higher spermine concentrations assembled from intermediates, similar to those formed at low spermine concentrations (Figure 51).

At each spermine concentration, the final assembly products were stable at both low (4°C) and warm (37°C) temperatures. The C-terminal domain of tubulin interacts with spermine at 2:1 spermine/C-terminal tail stoichiometry on two separated binding regions. The increasing spermine/tubulin molar ratio in this study, and the multiple associations of the observed assemblies, imply that spermine has numerous potential binding sites with varying affinities. The phases revealed here differ from the classical twisted-ribbon, helical, and tubular self- assembled structures. Although there is currently no theory that can explain conical-spiral-based assemblies, the self- association versatility of tubulin provides a fascinating means to design and create a wide range of building blocks for biomaterial applications.