Platelet Septins: Interaction Of The Human Septins Sept5, Sept7 And Sept11

Abstract Septins are GTP-binding proteins which form heteropolymeric complexes. In non-dividing cells (such as platelets and neurons) septins are implicated in exocytosis. The SEPT4, SEPT5 and SEPT8 are expressed in platelets. Platelets from a SEPT5 knockout mouse showed an altered serotonin secretion and platelet aggregation suggesting that SEPT5 is involved in secretion in platelets. Transmission electron microscopy of platelets revealed that SEPT4, SEPT5 and SEPT8 are localized surrounding alpha-granules suggesting that the three septins may be components of the septin complex in platelets and contribute in such a way to platelet biology. Activation of platelets by agonists resulted in the translocation of SEPT4 and SEPT8 to the platelet surface indicating a possible functional role of these proteins in granular secretion. Previously, we identified the interaction of SEPT5 with SEPT8 and showed that SEPT5 partners with SEPT11. The aim of this study was to identify other interaction partners of SEPT11. Using the yeast two-hybrid system we demonstrate that SEPT11 partners with SEPT7. Western analysis revealed that SEPT7 is also expressed in platelets. The molecular interaction of SEPT11 with SEPT7 was verified by precipitation of the SEPT7/SEPT11 complex from lysates of human platelets. Since SEPT5, SEPT7 and SEPT11 are members of the same septin complex and since SEPT5, SEPT7 and SEPT11 are expressed in platelets, SEPT5, SEPT7 and SEPT11 may play an important role in exocytosis in platelets.