Function of the TolC-like HgdD in Anabaena sp. strain PCC 7120

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We have developed methods for the analysis of transmembrane β-barrel polypeptide transporters from the filamentous cyanobacterium Anabaena sp. PCC 7120. We identified and initially characterized a TolC-like protein, HgdD, essential for formation of mature heterocysts, cells specialized for N2 fixation. The protein itself is present in both cell-types, vegetative cells and heterocysts. Its function in cell differentiation is most likely related to a remodelling of certain complexes between this TolC and the plasma membrane anchored machinery. On basis of a clear phenotype of hgdD mutants – lack of the heterocyst specific envelope – we proposed candidates for complex formation with TolC. In a preliminary analysis of the secretome the first candidate putatively transported by HgdD was identified. Now biophysical, biochemical and molecular biological characterization of this β-barrel type transporter and the machinery at the plasma membrane involved in the transport process will be conducted to further explore the function of outer membrane proteins in heterocyst development. In this study, substrate determination and analysis of the interaction between the plasma and outer membrane localized parts of the complex are in focus. The results will enable us to understand the functional circuit of the TolC protein and will stimulate the research on the formation of heterocyst specific layers during cell differentiation.