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

我们已经开发了用于分析来自丝状蓝藻鱼腥藻PCC 7120的跨膜β-桶多肽转运蛋白的方法。我们确定并初步表征了TolC样蛋白，HgdD，形成成熟的异形胞，专门用于N2固定的细胞所必需的。蛋白质本身存在于两种细胞类型，营养细胞和异形胞中。其在细胞分化中的功能最可能与该TolC和质膜锚定机构之间的某些复合物的重塑有关。基于hgdD突变体的明确表型-缺乏异形胞特异性包膜-我们提出了与TolC形成复合物的候选物。在对分泌组的初步分析中，鉴定了由HgdD转运的第一个候选质粒。现通过对这种β-桶型转运蛋白的生物物理、生化和分子生物学特性的研究，以及在细胞膜上参与转运过程的机制，进一步探讨外膜蛋白在异形胞发育中的作用。在这项研究中，基板之间的相互作用的血浆和外膜的复杂的局部部分的确定和分析是重点。这些结果将使我们能够了解TolC蛋白的功能电路，并将促进对细胞分化过程中异形胞特异性层形成的研究。

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.