Mutations in the major gas vesicle protein GvpA and impacts on gas vesicle formation in Haloferax volcanii.

Gas vesicles are proteinaceous, gas-filled nanostructures produced by some bacteria and archaea. The hydrophobic major structural protein GvpA forms the ribbed gas vesicle wall. An in-silico 3D-model of GvpA of the predicted coil-α1-β1-β2-α2-coil structure is available and implies that the two β-chains constitute the hydrophobic interior surface of the gas vesicle wall. To test the importance of individual amino acids in GvpA we performed 85 single substitutions and analyzed these variants in Haloferax volcanii ΔA + A transformants for their ability to form gas vesicles (Vac phenotype). In most cases, an alanine substitution of a non-polar residue did not abolish gas vesicle formation, but the replacement of single non-polar by charged residues in β1 or β2 resulted in Vac transformants. A replacement of residues near the β-turn altered the spindle-shape to a cylindrical morphology of the gas vesicles. Vac transformants were also obtained with alanine substitutions of charged residues of helix α1 suggesting that these amino acids form salt-bridges with another GvpA monomer. In helix α2, only the alanine substitution of His53 or Tyr54, led to Vac transformants, whereas most other substitutions had no effect. We discuss our results in respect to the GvpA structure and data available from solid-state NMR.