Supramolecular organization of Hfq-like proteins

Bacterial Hfq proteins are structural homologs of archaeal and eukaryotic Sm/Lsm proteins, which are characterized by a 5-stranded β-sheet and an N-terminal α-helix. Previously, it was shown that archaeal Lsm proteins (SmAP) could produce long fibrils spontaneously, in contrast to the Hfq from Escherichia coli that could form similar fibrils only after special treatment. The organization of these fibrils is significantly different, but the reason for the dissimilarity has not been found. In the present work, we studied the process of fibril formation by bacterial protein Hfq from Pseudomonas aeruginosa and archaeal protein SmAP from Methanococcus jannaschii. Both proteins have high homology with E. coli Hfq. We found that Hfq from P. aeruginosa could form fibrils after substitutions in the conserved Sm2 motif only. SmAP from M. jannaschii, like other archaeal Lsm proteins, form fibrils spontaneously. Despite differences in the fibril formation conditions, the architecture of both was similar to that described for E. coli Hfq. Therefore, universal nature of fibril architecture formed by Hfq proteins is suggested.