Structural characteristics of halobacterial gas vesicles

Abstract

Gas vesicle formation in halophilic archaea is encoded by a DNA region (the vac region) containing 14 different genes: gvpACNO and gvpDEFGHIJKLM. In Halobacterium salinarum PHH1 (which expresses the p-vac region from plasmid pHH1), gas vesicles are spindle shaped, whereas predominantly cylindrical gas vesicles are synthesized by the chromosomal c-vac region of H. salinarum PHH4 and the single chromosomal mc-vac region of Haloferax mediterranei. Homologous complementation of gvp gene clusters derived from the chromosomal c-vac region led to cylindrical gas vesicles in transformants and proved that the activity of the c-gvpA promoter depended on a gene product from the c-gvpE-M DNA region. Heterologous complementation experiments with transcription units of different vac regions demonstrated that the formation of chimeric gas vesicles was possible. Comparison of micrographs of wild-type and chimeric gas vesicles indicated that the shape was not exclusively determined by GvpA, the major structural protein of the gas vesicle wall. More likely, a dynamic equilibrium of several gvp gene products was responsible for determination of the shape. Transmission electron microscopy of frozen hydrated, wild-type gas vesicles showed moiré patterns due to the superposition of the front and back parts of the ribbed gas vesicle envelope. Comparison of projections of model helices with the moiré pattern seen on the cylindrical part of the gas vesicles provided evidence that the ribs formed a helix of low pitch and not a stack of hoops.

Use of a halobacterial bgaH reporter gene to analyse the regulation of gene expression in halophilic archaea

“…The inability of pGvpE to activate the c-gvpA promoter has already been recognized during heterologous complementation studies using the p-gvpDEFGHIJKLM unit of the p-vac region to complement the c-gvpACNO genes in Hf. volcanii transformants : no GvpA formation could be observed, suggesting that pGvpE cannot activate the c-gvpA promoter (Offner et al, 1998). This could also be the reason that gas vesicles of Hb.…”

Exploiting genomic patterns to discover new supramolecular protein assemblies

“…These proteins assemble into a continuous helical ring that encircles the cylindrical body. 53 It has been suggested that various ratios of these paralogs may modulate local shell architecture, such as cylinder radius and tip shape. 54 The small Hsp20 heat-shock proteins (or alphaHsps) are able to form large oligomeric structures with multiple paralogs.…”

“…35 Their structure is that of a cylinder, capped with cones at each end. 53 They are composed primarily of a paralogous family of proteins such as GvpA, GvpJ, and GvpM, some of which occur with additional copies, 54 often encoded within two back-toback, divergently transcribed operons [see Fig. 3(A)].…”

Analysis of tryptic digests indicates regions of GvpC that bind to gas vesicles of Anabaena flos-aquae

“…The wall of the cylinder and caps is 2 nm thick and is formed by ribs of width 4?6 nm, which in halobacterial gas vesicles (Offner et al, 1998) have been shown to represent turns of a shallow spiral. The gas vesicle is rigid (Walsby, 1982) and highly permeable to gases (Walsby, 1969) but impermeable to liquid water, which is excluded by the hydrophobic nature of the inside surface (Worcester, 1975).…”