These proteins are involved in the formation of gas vesicles ([1]).

1: Three different but related gene clusters encoding gas vesicles in halophilic archaea. Englert C, Kruger K, Offner S, Pfeifer F; J Mol Biol 1992;227:586-592. PMID:1404376

2: New Knowledge from Old: In silico discovery of novel protein domains in Streptomyces coelicolor. Yeats C, Bentley S, Bateman A; BMC Microbiol 2003;3:3-3. PMID:12625841