<i>Staphylococcus aureus</i> FtsZ and PBP4 bind to the conformationally dynamic N-terminal domain of GpsB.

Abstract

In the Firmicutes phylum, GpsB is a membrane associated protein that coordinates peptidoglycan synthesis with cell growth and division. Although GpsB has been studied in several bacteria, the structure, function, and interactome of <i>Staphylococcus aureus</i> GpsB is largely uncharacterized. To address this knowledge gap, we solved the crystal structure of the N-terminal domain of <i>S. aureus</i> GpsB, which adopts an atypical, asymmetric dimer, and demonstrates major conformational flexibility that can be mapped to a hinge region formed by a three-residue insertion exclusive to <i>Staphylococci</i>. When this three-residue insertion is excised, its thermal stability increases, and the mutant no longer produces a previously reported lethal phenotype when overexpressed in <i>Bacillus subtilis</i>. In <i>S. aureus</i>, we show that these hinge mutants are less functional and speculate that the conformational flexibility imparted by the hinge region may serve as a dynamic switch to fine-tune the function of the GpsB complex and/or to promote interaction with its various partners. Furthermore, we provide the first biochemical, biophysical, and crystallographic evidence that the N-terminal domain of GpsB binds not only PBP4, but also FtsZ, through a conserved recognition motif located on their C-termini, thus coupling peptidoglycan synthesis to cell division. Taken together, the unique structure of <i>S. aureus</i> GpsB and its direct interaction with FtsZ/PBP4 provide deeper insight into the central role of GpsB in <i>S. aureus</i> cell division.