Protein Gas Vesicles of <i>Bacillus megaterium</i> as Enhancers of Ultrasound-Induced Transcriptional Regulation.

Abstract

Gas vesicles (GVs) are large cylindrical gas-filled protein assemblies found in diverse aquatic bacteria that enable their adaptation of buoyancy. GVs have already been used as ultrasound contrasting agents. Here, we investigate GVs derived from <i>Bacillus megaterium</i>, aiming to minimize the number of accessory Gvps within the GV gene cluster and demonstrate the use of GVs as enhancers of acoustic radiation force administered by ultrasound. Three (<i>GvpR</i>, <i>GvpT</i>, and <i>GvpU</i>) out of 11 genes in the cluster were found to be dispensable for functional GV formation, and their omission resulted in narrower GVs. Two essential proteins GvpJ and GvpN were absent from recently determined GV structures, but GvpJ was nevertheless found to be tightly bound to the cylindrical part of GVs in this study. Additionally, the N-terminus of GvpN was observed to play an important role in the formation of mature GVs. The binding of engineered GvpC from<i>Anabaena flos-aquae</i> to HEK293 cells via integrins enhanced the acoustic force delivered by ultrasound and resulted in an increased Ca²⁺ influx into cells. Coupling with a synthetic Ca²⁺-dependent signaling pathway GVs efficiently enhanced cell stimulation by ultrasound, which expands the potentials of noninvasive sonogenetics cell stimulation.