An alkali-inducible flotillin-like protein from Bacillus halodurans C-125

Flotillins are markers of lipid microdomains, and have emerged as a key concept in cellular biology. However, it remains unclear whether flotillin proteins exist in prokaryotic cells. The amino acid sequence of the BH3500 protein from Bacillus halodurans was 30% identical to that of flotillin-1. Motif analysis revealed that several specific residues (SPFH and flotillin domains, an AEA-repeat structure) and five potential phosphorylation sites are conserved in the BH3500 protein. In addition, the BH3500 protein was found to possess two transmembrane-spanning domains at the N-terminus, which is consistent with the common properties of flotillin-1. The BH3500 protein was detected in the Triton-insoluble, buoyant membrane fraction of B. halodurans by mass spectrometry and Western blotting. Interestingly, BH3500 was expressed strongly in alkaline conditions at both transcriptional and translational levels, which implies that it is one of the alkali-inducible proteins.