US EPA

1337379 

Journal Article 

Transmembrane topology of the Acr3 family arsenite transporter from Bacillus subtilis 

Aaltonen, EKJ; Silow, M 

2008 

1 

Biochimica et Biophysica Acta. Biomembranes
ISSN: 0005-2736
EISSN: 1879-2642 

1778 

4 

963-973 

English 

18088595 

10.1016/j.bbamem.2007.11.011 

WOS:000255228000017 

The transmembrane topology of the Acr3 family arsenite transporter Acr3 from Bacillus subtilis was analysed experimentally using translational fusions with alkaline phosphatase and green fluorescent protein and in silico by topology modelling. Initial topology prediction resulted in two models with 9 and 10 TM helices respectively. 32 fusion constructs were made between truncated forms of acr3 and the reporter genes at 17 different sites throughout the acr3 sequence to discriminate between these models. Nine strong reporter protein signals provided information about the majority of the locations of the cytoplasmic and extracellular loops of Acr3 and showed that both the N- and the C-termini are located in the cytoplasm. Two ambiguous data points indicated the possibility of an alternative 8 helix topology. This possibility was investigated using another 10 fusion variants, but no experimental support for the 8 TM topology was obtained. We therefore conclude that Acr3 has 10 transmembrane helices. Overall, the loops which connect the membrane spanning segments are short, with cytoplasmic loops being somewhat longer than the extracellular loops. The study provides the first ever experimentally derived structural information on a protein of the Acr3 family which constitutes one of the largest classes of arsenite transporters. 

arsenite; transmembrane topology; Acr3; translational fusion; alkaline phosphatase; GFP