Biochemical and Cell Biological Analyses of a Mammalian Septin Complex, Sept7/9b/11

Abstract

Septins are members of a conserved family of cytoskeletal GTPases present in organisms as diverse as yeast and mammals. Unlike lower eukaryotic cells, the physiological significance of mammalian septin complexes is largely unknown. Using specific antibodies, we found at least five septins, Sept2, Sept7, Sept8, Sept9b, and Sept11, in septin complexes affinity-purified with anti-Sept7 antibody-conjugated column from rat embryonic fibroblast REF52 cells. Immunofluorescence studies revealed co-localization of Sept7, Sept9b, and Sept11 along stress fibers in REF52 cells. Biochemical and immunoprecipitation analyses revealed that the three septins directly bind with each other through their N-or C-terminal divergent regions. These septins per se formed distinct and characteristic filament structures when transiently expressed in COS7 cells. When two of the three septins were coexpressed in COS7 cells, combination-dependent filament elongation, bundling, or disruption was observed. Taken together, our results suggest that septin filament structures may be affected by interactions with other septins included in the complex.

The expression pattern of SEPT7 correlates with sperm morphology

“…Septins form homo-and heterooligomeric complexes that are assembled into filamentous structures depending on the combination of the various septin members in mammals [1,34]. Considering the high similarity of the expression patterns of SEPT4, SEPT7, and SEPT12, it is highly likely that the SEPT4/7/12 complex not only constitutes the structural basis of the annulus but also serves as a diffusion barrier between the various subcellular compartments of mammalian spermatozoa [6,11,35,36].…”

Some assembly required: yeast septins provide the instruction manual

“…Some models are supported by data on individual septin-septin interactions [7,9,45]. In the human complex, Sept9 is shown as the counterpart of Cdc10 (Table 1), based on sequence similarity and phylogenetic-tree analysis [5], the lack of a CTE, and the association between Sept9 and both Sept11 (a Cdc3 ortholog) and Sept7 (a Cdc12 ortholog) [83]. The N-terminal domain of Sept9 is required for its interaction with Sept7 and Sept11, which is similar to the interaction of Cdc10 with Cdc3 and Cdc12.…”

“…If so, including Sept9 in the complexes should result in reconstituted filaments that are more stable, longer and more cross-braced. In any event, the fact that heterodimers of Sept9-Sept7 and Sept9-Sept11 (a close paralog of Sept6) form readily in vitro [83] shows that the human Cdc10-like septin associates, as does yeast Cdc10, with Cdc3-like and Cdc12-like partners.…”

“…The N-terminal domain of Sept9 is required for its interaction with Sept7 and Sept11, which is similar to the interaction of Cdc10 with Cdc3 and Cdc12. However, there is evidence that the C-terminal portions of Sept7 and of Sept11 are required for their interaction with Sept9 [83], unlike the interactions of Cdc3 and Cdc12 with Cdc10 [10]. Schematic depiction of septin recruitment and septin-collar formation during the cell cycle of budding yeast.…”

Septin 11 Restricts InlB-mediated Invasion by Listeria

“…In the SEPT7-SEPT6-SEPT2-SEPT2-SEPT6-SEPT7 complex, SEPT2 has a central role in filament formation (9), whereas SEPT6 is thought to be replaceable with other SEPT6 group members, including SEPT11 (3). Widely expressed in mammalian tissues (10), SEPT11 may also be a substitute for SEPT6 in other mammalian septin complexes such as SEPT7-SEPT9-SEPT11 (10) or SEPT5-SEPT7-SEPT11 (11). Because other septins homologous to SEPT11 might compensate for its deficiency (12), the degree to which SEPT11 is required for septin filament structure and function is not yet known.…”