*Article* **The C Terminus of the Ribosomal-Associated Protein LrtA Is an Intrinsically Disordered Oligomer**

**José L. Neira 1,2,\*,†, A. Marcela Giudici 1,†, Felipe Hornos 1, Arantxa Arbe <sup>3</sup> and Bruno Rizzuti 4,\***


Received: 14 November 2018; Accepted: 2 December 2018; Published: 5 December 2018

**Abstract:** The 191-residue-long LrtA protein of *Synechocystis* sp. PCC 6803 is involved in post-stress survival and in stabilizing 70S ribosomal particles. It belongs to the hibernating promoting factor (HPF) family, intervening in protein synthesis. The protein consists of two domains: The N-terminal region (N-LrtA, residues 1–101), which is common to all the members of the HPF, and seems to be well-folded; and the C-terminal region (C-LrtA, residues 102–191), which is hypothesized to be disordered. In this work, we studied the conformational preferences of isolated C-LrtA in solution. The protein was disordered, as shown by computational modelling, 1D-1H NMR, steady-state far-UV circular dichroism (CD) and chemical and thermal denaturations followed by fluorescence and far-UV CD. Moreover, at physiological conditions, as indicated by several biochemical and hydrodynamic techniques, isolated C-LrtA intervened in a self-association equilibrium, involving several oligomerization reactions. Thus, C-LrtA was an oligomeric disordered protein.

**Keywords:** disordered protein; folding; oligomer; ribosomal protein; protein stability
