LAUSR

Intrinsically disordered regions (IDRs) can function as autoregulators of folded enzymes to which they are tethered. One example is the bacterial cell division protein, FtsZ. This includes a folded core and a C-terminal tail (CTT) that encompasses a poorly conserved, disordered C-terminal linker (CTL) and a well-conserved 17-residue 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 basis of autoregulatory functions of the CTT in Bacillus subtilis FtsZ (Bs-FtsZ). Molecular simulations show that the CT17 of Bs- FtsZ makes statistically significant CTL-mediated contacts with the T7 loop. Statistical Coupling Analysis of more than 103 sequences from FtsZ orthologs reveals clear covariation of the T7 loop and the CT17 with most of the core domain whereas the CTL is under independent selection. Despite this, we discover the conservation of non-random sequence patterns within CTLs across orthologs. 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 non-random, functionally relevant sequence patterns that also preserve three-way covariation of the CT17, the T7 loop, and core domain. Significance Statement Z-ring formation by the protein FtsZ controls cell division in rod-shaped bacteria. The C-terminus of FtsZ encompasses a disordered C-terminal linker (CTL) and a conserved CT17 motif. Both modules are essential for Z-ring formation and proper localization of FtsZ in cells. Previous studies suggested that generic intrinsically disordered regions (IDRs) might be suitable functional replacements for naturally occurring CTLs. Contrary to this suggestion, we find that the sequence-encoded conformational properties of CTLs help mediate autoregulatory interactions between covarying regions within FtsZ. Functional properties of the CTL are encoded via evolutionarily conserved, non-random sequence patterns. Disruption of these patterns impair molecular functions and cellular phenotypes. Our findings have broad implications for discovering functionally consequential sequence features within IDRs of other proteins.