Lysinoalanine crosslinking in the extracellular flagellar hook of Synergistota.

Thermanaerovibrio acidaminovorans hook protein FlgE forms lysinoalanine (Lal) crosslinks, analogous to spirochetes, in wild-type cell culture and in vitro.

• Why it matters: Lal crosslinking in spirochetes is linked to flagellar motility, but it was unclear whether extracellular-flagellated bacteria also use the same stabilizing modification.
• What they did: A bioinformatic screen for conserved Lal catalytic residues guided biochemical crosslinking assays and high-resolution mass spectrometry to test Lal formation by FlgE from Thermanaerovibrio acidaminovorans.
• The result: Lal crosslinks were detected in FlgE from Thermanaerovibrio acidaminovorans in vitro and in wild-type cell culture, establishing the first example outside the spirochete phylum and suggesting broader conservation.

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