This mechanism is independent of the N-terminal A domain (Angelini et al., 2006; Braig et al., 2009). To verify that the observed membrane association was not an artifact of increased protein levels, we treated the membrane fraction with 0.2 M Na2CO3. It has been reported that this treatment is able to remove peripherally associated proteins from the membrane (de Leeuw selleck inhibitor et al., 1997). As shown in Fig. 1b, the association between ScFtsY1-412 and the membrane was completely resistant to the
carbonate treatment. ScFtsY11-412 also exhibited strong carbonate resistance. In contrast, more than half of the membrane-associated proteins were extracted from membrane fraction and were detected in the soluble fraction after carbonate treatment in the ScFtsY36-412 and ScFtsY40-412 samples. These results were consistent with our previous
observations, which demonstrated that residues 11–35 contributed significantly to the membrane-targeting capability of ScFtsY. These residues bind tightly to the membrane. Without them, a fraction of the mutant ScFtsY proteins could still target the membrane (potentially through the NG domain-mediated protein-protein interaction), but the binding between membrane and protein was significantly weaker. To fully establish Roscovitine concentration the membrane-targeting role of the N-terminal sequence of ScFtsY, we examined whether this region alone was capable of directing EGFP to the membrane. EGFP is a soluble protein located entirely in the cytosol. We attached portions of the ScFtsY N-terminal sequence to EGFP and measured
the subcellular localization of the resulting constructs. To minimize structural change Thymidine kinase to EGFP, the linker LPEPGLPEPG was used to link the ScFtsY N-terminal sequences to the N-terminus of EGFP. Three constructs were made. These constructs included the ScFtsY11-39, ScFtsY11-35, and ScFtsY11-24 fragments. In addition, a construct carrying the E. coli N-terminal sequence 1–14 (EcFtsY1-14) was made as a negative control (Fig. 2). The subcellular localizations of the four recombinant proteins were assessed using the same protocol as before (Fig. 2). Results showed that ScFtsY11-39 tagged EGFP was localized almost exclusively to the membrane. ScFtsY11-35, which lacks the four successive positively charged residues, was primarily located in the membrane fraction, although a small proportion of this protein was clearly detectable in the soluble fraction. ScFtsY11-24, which consists of the 14 hydrophobic residues at the N-terminal of ScFtsY, was able to target about half of the recombinant EGFP to the membrane. The association between recombinant EGFPs and the membrane was strong. Carbonate treatment could not extract ScFtsY11-39-EGFP proteins from the membrane. However, a noticeable proportion of the membrane-bound ScFtsY11-35-EGFP could be extracted from the membrane.