<p> Bacterial cell division is an essential process, which is initiated by forming the Z-ring as a cytoskeletal scaffold at the midcell site, followed by the recruitment of a series of divisome proteins. In <i>Escherichia coli</i> (Ec), at least 15 divisome proteins (FtsZ, FtsA, ZipA, FtsK, FtsQ, FtsB, FtsL, FtsI, FtsW, FtsN, FtsE, FtsX, ZapA, AmiC, EnvC) have been implicated in this process. The components of the cell division machinery proteins in <i>Neisseria gonorrhoeae</i> (Ng) differs from <i>E. coli. N. gonorrhoeae</i> possesses FtsA, but lacks FtsB. ZipA and FtsL in <i>N. gonorrhoeae</i> have low identity to ZipA and FtsL from <i>E. coli</i>. Our laboratory has studied the central division protein FtsZ in <i>N. gonorrhoeae</i>. Thus, my research investigated the role of <i>N. gonorrhoeae</i> FtsA in cell division and investigated the interactions between divisome proteins from <i>N. gonorrhoeae</i> to understand divisome assembly.</p> <p>This study determined the association of FtsA_Ng with FtsZ</sub>Ng and other divisome proteins in <i>N. gonorrhoeae</i> and identified the functional domains of FtsA<sun>Ng</sub> involved in these interactions using a bacterial two-hybrid (B2H) assay. FtsA_Ng interacted with FtsZ_Ng, FtsK_Ng, FtsW_Ng, FtsQ_Ng, and FtsN_Ng. Self-interactions of FtsA_Ng and FtsZ_Ng were also detected. FtsI_Ng, FtsE_Ng and FtsX_Ng did not interact with FtsA_Ng. The 2A₁, 2A₂ and 2B domains of FtsA_Ng were sufficient to interact with FtsZ_Ng independently. Domain 2A₁ interacted with FtsK_Ng and FtsN_Ng. Domain 2B of FtsA_Ng interacted with FtsK_Ng, FtsQ_Ng, and FtsN_Ng. Domain 2A₂ of FtsA_Ng interacted with FtsQ_Ng, FtsW_Ng, and FtsN_Ng. These data suggest that FtsA in <i>N. gonorrhoeae</i> plays a key role in interactions with FtsZ and other divisome proteins.</p> <p>The potential interactions between divisome proteins in <i>N. gonorrhoeae</i> were examined using B2H assays. The comparisons between the <i>N. gonorrhoeae</i> divisome protein interaction network and those of <i>E. coli</i> and <i>S. pneumoniae</i> indicates that the divisome protein interactome of <i>N. gonorrhoeae</i> is more similar to that of <i>S. pneumoniae</i> and differs from that of <i>E. coli</i>. The comparisons revealed that compared to the interactions in <i>E. coli</i> and <i>S. pneumoniae</i>, more interactions between divisome proteins upstream of FtsA_Ng (including FtsA_Ng) and downstream of FtsA_Ng were observed in <i>N. gonorrhoeae</i> while fewer interactions between divisome proteins downstream of FtsA_Ng were observed in <i>N. gonorrhoeae</i>. Possible reasons for this include the inability of ZipA_Ng to interact with other divisome proteins and the absence of FtsL and FtsB in <i>N. gonorrhoeae</i>, resulting in the lack of an FtsQ-FtsB-FtsL complex in <i>N. gonorrhoeae</i>. These results indicate a possibly different divisome assembly in <i>N. gonorrhoeae</i> from that proposed models for <i>E. coli</i>.</p> A model for FtsA_Ng structure was predicted based on structural homology modeling with the resolved crystal structure of <i>Thermotoga maritima</i> FtsA. Four domains on the molecule were identified, designated 1A, 1C, 2B and 2A (including 2A₁ and 2A₂). Domains 2A and 2B of FtsA were highly conserved based on multi-sequence alignments of FtsAs from 30 bacteria. FtsA_Ng located to the division site in <i>N. gonorrhoeae</i> cells and the ratio of FtsA to FtsZ ranged from 1:24 to 1: 33 in three <i>N. gonorrhoeae</i> strains, which gave a lower cellular concentration of FtsA compared to other organisms.</p> <p>I also determined that overexpression of FtsA_Ng in <i>E. coli</i> led to cell filamentous in rod-shaped <i>E. coli</i> and cell enlargement and aggregation in mutant, round <i>E. coli</i>. FtsA_Ng failed to complement an <i>ftsA</i>_Ec-deletion <i>E. coli</i> strain although the overexperssion of FtsA_Ng disrupted <i>E. coli</i> cell division. In addition, overexpression of FtsA_Ng only affected cell division in some cells and its localization in <i>E. coli</i> was independent of interaction with <i>E. coli</i> FtsA or FtsZ. These results indicate that FtsA_Ng exhibits a species-specific functionality and <i>E. coli</i> is not a suitable model for studying FtsA_Ng functionality.</p> <p>This is the first study to characterize FtsA from <i>N. gonorrhoeae</i> in cell division. I identified novel functional domains of FtsA_Ng involved in interactions with other divisome proteins. The <i>N. gonorrhoeae</i> divisome protein interaction network determined by B2H assays provides insight into divisome assembly in <i>N. gonorrhoeae</i></p>.

<p> Bacterial cell division is an essential process, which is initiated by forming the Z-ring as a cytoskeletal scaffold at the midcell site, followed by the recruitment of a series of divisome proteins. In <i>Escherichia coli</i> (Ec), at least 15 divisome proteins (FtsZ, FtsA, ZipA, FtsK, FtsQ, FtsB, FtsL, FtsI, FtsW, FtsN, FtsE, FtsX, ZapA, AmiC, EnvC) have been implicated in this process. The components of the cell division machinery proteins in <i>Neisseria gonorrhoeae</i> (Ng) differs from <i>E. coli. N. gonorrhoeae</i> possesses FtsA, but lacks FtsB. ZipA and FtsL in <i>N. gonorrhoeae</i> have low identity to ZipA and FtsL from <i>E. coli</i>. Our laboratory has studied the central division protein FtsZ in <i>N. gonorrhoeae</i>. Thus, my research investigated the role of <i>N. gonorrhoeae</i> FtsA in cell division and investigated the interactions between divisome proteins from <i>N. gonorrhoeae</i> to understand divisome assembly.</p> <p>This study determined the association of FtsA_Ng with FtsZ</sub>Ng and other divisome proteins in <i>N. gonorrhoeae</i> and identified the functional domains of FtsA<sun>Ng</sub> involved in these interactions using a bacterial two-hybrid (B2H) assay. FtsA_Ng interacted with FtsZ_Ng, FtsK_Ng, FtsW_Ng, FtsQ_Ng, and FtsN_Ng. Self-interactions of FtsA_Ng and FtsZ_Ng were also detected. FtsI_Ng, FtsE_Ng and FtsX_Ng did not interact with FtsA_Ng. The 2A₁, 2A₂ and 2B domains of FtsA_Ng were sufficient to interact with FtsZ_Ng independently. Domain 2A₁ interacted with FtsK_Ng and FtsN_Ng. Domain 2B of FtsA_Ng interacted with FtsK_Ng, FtsQ_Ng, and FtsN_Ng. Domain 2A₂ of FtsA_Ng interacted with FtsQ_Ng, FtsW_Ng, and FtsN_Ng. These data suggest that FtsA in <i>N. gonorrhoeae</i> plays a key role in interactions with FtsZ and other divisome proteins.</p> <p>The potential interactions between divisome proteins in <i>N. gonorrhoeae</i> were examined using B2H assays. The comparisons between the <i>N. gonorrhoeae</i> divisome protein interaction network and those of <i>E. coli</i> and <i>S. pneumoniae</i> indicates that the divisome protein interactome of <i>N. gonorrhoeae</i> is more similar to that of <i>S. pneumoniae</i> and differs from that of <i>E. coli</i>. The comparisons revealed that compared to the interactions in <i>E. coli</i> and <i>S. pneumoniae</i>, more interactions between divisome proteins upstream of FtsA_Ng (including FtsA_Ng) and downstream of FtsA_Ng were observed in <i>N. gonorrhoeae</i> while fewer interactions between divisome proteins downstream of FtsA_Ng were observed in <i>N. gonorrhoeae</i>. Possible reasons for this include the inability of ZipA_Ng to interact with other divisome proteins and the absence of FtsL and FtsB in <i>N. gonorrhoeae</i>, resulting in the lack of an FtsQ-FtsB-FtsL complex in <i>N. gonorrhoeae</i>. These results indicate a possibly different divisome assembly in <i>N. gonorrhoeae</i> from that proposed models for <i>E. coli</i>.</p> A model for FtsA_Ng structure was predicted based on structural homology modeling with the resolved crystal structure of <i>Thermotoga maritima</i> FtsA. Four domains on the molecule were identified, designated 1A, 1C, 2B and 2A (including 2A₁ and 2A₂). Domains 2A and 2B of FtsA were highly conserved based on multi-sequence alignments of FtsAs from 30 bacteria. FtsA_Ng located to the division site in <i>N. gonorrhoeae</i> cells and the ratio of FtsA to FtsZ ranged from 1:24 to 1: 33 in three <i>N. gonorrhoeae</i> strains, which gave a lower cellular concentration of FtsA compared to other organisms.</p> <p>I also determined that overexpression of FtsA_Ng in <i>E. coli</i> led to cell filamentous in rod-shaped <i>E. coli</i> and cell enlargement and aggregation in mutant, round <i>E. coli</i>. FtsA_Ng failed to complement an <i>ftsA</i>_Ec-deletion <i>E. coli</i> strain although the overexperssion of FtsA_Ng disrupted <i>E. coli</i> cell division. In addition, overexpression of FtsA_Ng only affected cell division in some cells and its localization in <i>E. coli</i> was independent of interaction with <i>E. coli</i> FtsA or FtsZ. These results indicate that FtsA_Ng exhibits a species-specific functionality and <i>E. coli</i> is not a suitable model for studying FtsA_Ng functionality.</p> <p>This is the first study to characterize FtsA from <i>N. gonorrhoeae</i> in cell division. I identified novel functional domains of FtsA_Ng involved in interactions with other divisome proteins. The <i>N. gonorrhoeae</i> divisome protein interaction network determined by B2H assays provides insight into divisome assembly in <i>N. gonorrhoeae</i></p>.