Bioaccumulation of heavy metals with protein fusions of metallothionein tobacterial OMPs

In view of potential biotechnological applications, eukaryotic metallothion eins (MTs) have been expressed in Escherichia coli as fusions to membrane o r membrane-associated proteins such as LamB, the peptidoglycan-associated l ipoprotein protein (PAL) or a hybrid Lpp/OmpA carrier sequence. The use of different anchors enables the MT moiety to be targeted into various cell co mpartments thus bringing the metal-binding ability of the resulting hybrids to specific sites of the cell structure. To this end, both full-size and p artial sequences of the human or mouse MTs have been genetically fused to: i) the permissive site 153 of the LamB sequence, which loops out the MT to the external medium; ii) the N-terminus of a PAL variant devoid of its N-te rminal cystein, which targets expression of the fusion into the periplasm; and iii) the C-terminus of Lpp-OmpA, for anchoring the MT to the outer memb rane protein as an N-terminal fusion. Each type of fusion presented a disti nct behavior in terms of expression, stability and ability to endow E. coli cells an enhanced accumulation of Cd2+, in good correlation with the numbe r of metal-binding centers contributed by the MT moiety of the fusions. The expression in vivo of metalloproteins bound to bacterial envelope structur es opens a way to design biomass with specific metal-binding properties. (C ) Societe francaise de biochimie et biologie moleculaire / Elsevier, Paris.