3 9 I H I G H L I G H T S 2 0 2 1
PRINCIPAL PUBLICATION AND AUTHORS
Higher-order immunoglobulin repertoire restrictions in CLL: the illustrative case of stereotyped subsets 2 and 169, K. Gemenetzi (a,b), F. Psomopoulos (a,c), A.A. Carriles (d), M. Gounari (a), C. Minici (d), K. Plevova (e), L.A. Sutton (c), M. Tsagiopoulou (a), P. Baliakas (f), K. Pasentsis (a), A. Anagnostopoulos (g), R. Sandaltzopoulos (b), R. Rosenquist (c,h), F. Davi (i), S. Pospisilova (e), P. Ghia (j), K. Stamatopoulos (a,c), M. Degano (d), A. Chatzidimitriou (a,c), Blood 137, 14 1895-1904 (2021); https:/doi.org/10.1182/blood.2020005216 (a) Centre for Research and Technology Hellas, Thessaloniki (Greece) (b) Democritus University of Thrace, Alexandroupolis (Greece) (c) Karolinska Institutet, Stockholm (Sweden) (d) IRCCS Scientific Institute San Raffaele, Milan (Italy) (e) Masaryk University, Brno (Czech Republic) (f) Uppsala University, Uppsala (Sweden) (g) G. Papanikolaou Hospital, Thessaloniki (Greece) (h) Karolinska University Hospital, Stockholm (Sweden) (i) Hôpital Pitié-Salpêtrière and Sorbonne University, Paris (France) (j) Università Vita-Salute and IRCCS Ospedale San Raffaele (Italy)
 L. Scarfò et al., Crit. Rev. Oncol. Hematol. 104, 169-182 (2016).  C. Minici et al., Nat. Commun. 8, 15746 (2017).
Cryo-EM structures of the chikungunya virus nsP1 reveal capping rings as functional gates of membranous viral factories Cryo-electron microscopy structures of the chikungunya virus nsP1 protein reveal the structural basis of the coupling between membrane binding, oligomerisation and allosteric activation of the capping enzyme, which underpins the association of the viral replication machinery with virus-induced membranous organelles within host cells.
Studies of the replication complexes of positive-stranded RNA viruses have been hampered by their membrane association, making them elusive for structural studies. In this work, a membrane-bound complex from one of these
replication complexes, the chikungunya virus RNA capping protein, nsP1, was isolated. For decades, nsP1 was studied in its monomeric form, as it comes from E. coli recombinant expression. Using eukaryotic expression systems and detergents, homogeneous and very active ring-shaped complexes were obtained, in contrast with the poorly active monomeric nsP1. The complexes were prepared for single- particle cryo-EM structure determination and imaged at beamline CM01, enabling the 3D reconstruction of the nsP1 rings at 2.6-Å resolution.
The resulting cryo-EM structure revealed that nsP1 forms homo-dodecameric rings, defining three important regions in its architecture (Figure 25). The crown of the ring harbours the capping domains, which stack against each other to stabilise their active sites conformation. The capping domains have similar folding to homologous
Fig. 25: Atomic structure of the pores of the chikungunya nsP1 virus with the different monomers shown in different colours. Each atom is represented as a sphere. Left: the pore is shown from the cytoplasmic view; right: from a side view. The dimensions of the pore are indicated on the left; the crown, waist and skirt regions are indicated on the right, and the contact sites with the membrane are indicated at the bottom by dashed lines.