from: The Cell Biology of Cyanobacteria (Edited by: Enrique Flores and Antonia Herrero). Caister Academic Press, U.K. (2014)
Gas vesicles are hollow, organelles that provide buoyancy in aquatic prokaryotes and allow them to regulate their depth in the water column. Classic studies have shown them to be rigid and permeable to gases as large as C4F8. The wall of the hollow structure is formed entirely of protein. The principal component, GvpA (~ 7.5 kDa) is a metamorphic protein, adopting two conformations in an asymmetric dimer. These assemble into an amyloid (i.e., open-ended, cross-β) ribbon that wraps around the vesicle axis in a shallow helix and presents an aliphatic face to the interior. This aliphatic face is expected to cause evaporation of liquid water from the interior of nascent vesicles and prevent water condensation inside mature vesicles. A second protein GvpC, adheres to the GvpA shell and strengthens it. A great deal remains to be learned about how other members of the gvp gene cluster cooperate with the two main structural proteins in assembling and disassembling vesicles. Of particular interest is the fact that, despite the amyloid properties of the vesicles, the cells are able to dismantle them, in order to descend in the water column and apparently recycle protein from vesicles that have collapsed read more ...