Connecting sequence features within the disordered C-terminal linker of B. subtilis FtsZ to functions and bacterial cell division.

Abstract

Intrinsically disordered regions (IDRs) can function as autoregulators of folded enzymes to which they are tethered. One such example is the disordered C-terminal tail (CTT) of FtsZ, an essential GTPase in bacterial cell division. FtsZs feature a folded core and a CTT that encompasses a poorly conserved, disordered C-terminal linker (CTL) and a conserved 17-residues C-terminal peptide (CT17). Sites for GTPase activity of FtsZs are formed at the interface between GTP binding sites and T7 loops on cores of adjacent subunits within dimers. Here, we explore the molecular, evolutionary, and cellular bases for how autoregulatory functions of the CTT are realized in Bacillus subtilis FtsZ (Bs-FtsZ). Molecular simulations show statistically significant CTL-mediated contacts between the T7 loop and the CT17. Statistical coupling analysis of more than 1000 orthologs reveals clear covariation of the T7 loop and the CT17 with most of the core domain whereas the CTL is under independent selection. Furthermore, we also identify a conserved set of non-random sequence patterns within the CTLs, including linear clustering of polar and acidic residues, that modulate the interaction between the core and the CTT. To test how the non-random patterns of CTLs mediate CTT-core interactions and modulate FtsZ functionalities, we designed Bs-FtsZ variants by altering the patterning of oppositely charged residues within the CTL. Such alterations disrupt the core-CTT interactions, lead to anomalous assembly and inefficient GTP hydrolysis in vitro, and protein degradation, aberrant assembly, and disruption of cell division in vivo. Our findings suggest that viable CTLs in FtsZs are likely to be IDRs that encompass the non-random, functionally relevant sequence patterns that also preserve three-way covariation of the CT17, the T7 loop, and core domain.