'GGFGGQ' repeats in Hfq of Acinetobacter baumannii are essential for nutrient utilization and virulence

The nosocomial pathogen Acinetobacter baumannii is known for causing lung and soft tissue infections in immunocompromised hosts. Its ability to adapt to various environments through post-transcriptional gene regulation is key to its success. Central to this regulation is the RNA chaperone Hfq, which facilitates interactions between mRNA targets and their small RNA partners through a Sm-core domain. Notably, the A. baumannii Hfq protein has a uniquely long C-terminal domain with "GGFGGQ" amino acid repeats and an acidic amino acid-rich C-terminal tip (C-tip). Previous research has shown the importance of the intact C-terminal domain for Hfq's functionality. Given the significance of the C-tip in Escherichia coli Hfq, we examined the pathophysiological roles of the redundant 'GGFGGQ' repeats along with the C-tip of A. baumannii Hfq. We constructed several variations of Hfq protein with fewer 'GGFGGQ' repeats while preserving the C-tip and variants with altered C-tip amino acid composition. We then studied their RNA interaction abilities and assessed the pathophysiological fitness and virulence of genome-complemented A. baumannii mutants. Our findings reveal that the redundancy of the 'GGFGGQ' repeats is crucial for Hfq's role in pathophysiological fitness and negatively impacts A. baumannii's virulence in a murine lung infection model. In addition, C-tip mutants exhibited a negative effect on both fitness and virulence, however, to a lesser extent than the other variants. These results underscore the importance of 'GGFGGQ' redundancy and acidic residues in Hfq's ribo-regulation and autoregulation, suggesting their critical role in establishing regulatory networks.