The accessory gas vesicle protein GvpM of haloarchaea and its interaction partners during gas vesicle formation

Gas vesicles consist predominantly of the hydrophobic GvpA and GvpC, and the accessory proteins GvpF through GvpM are required in minor amounts during formation. GvpM and its putative interaction partners were investigated. GvpM interacted with GvpH, GvpJ and GvpL, but not with GvpG. Interactions were also observed in vivo in Haloferax volcanii transformants using Gvp fusions to the green fluorescent protein smGFP. Cells producing the hydrophobic MGFP contained a single fluorescent aggregate per cell, whereas cells containing LGFP or HGFP were fully fluorescent. The soluble LGFP formed stable co-aggregates with GvpM in LGFPM transformants, but the presence of GvpH resulted in the absence of MGFP foci in HMGFP transformants. Substitution- and deletion mutants of GvpM determined functionally important amino acids (aa). Substitution of a polar by a non-polar aa in the N-terminal region of GvpM had no effect, whereas a substitution of a non-polar by a polar aa in this region inhibited gas vesicle formation in transformants. Substitutions in region 44–48 of GvpM strongly reduced the number of gas vesicles, and deletions at the N-terminus resulted in Vac− transformants. Gas vesicle morphology was not affected by any mutation, implying that GvpM is required during initial stages of gas vesicle assembly.