TAILIEUCHUNG - Báo cáo khoa học: GTP binding and hydrolysis kinetics of human septin 2

Septins are a family of conserved proteins that are essential for cytokinesis in a wide range of organisms including fungi, Drosophila and mammals. In budding yeast, where they were first discovered, they are thought to form a filamentous ring at the bridge between the mother and bud cells. | iFEBS Journal GTP binding and hydrolysis kinetics of human septin 2 Yi-Wei Huang1 Mark C. Surka1 3 Denis Reynaud2 Cecil Pace-Asciak2 and William S. Trimble1 3 1 Program in Cell Biology Hospitalfor Sick Children Toronto ON Canada 2 Program in Integrative Biology Hospitalfor Sick Children Toronto ON Canada 3 Department of Biochemistry University of Toronto ON Canada Keywords casein kinase II GTP GTPase kinetics phosphorylation septins Correspondence W. Trimble Program in Cell Biology Hospitalfor Sick Children 555 University Avenue Toronto Ontario M5G 1X8 Canada Fax 1 416 8135028 Tel 1 416 8136889 E-mail wtrimble@ Received 24 February 2006 revised 8 May 2006 accepted 22 May 2006 doi Septins are a family of conserved proteins that are essential for cytokinesis in a wide range of organisms including fungi Drosophila and mammals. In budding yeast where they were first discovered they are thought to form a filamentous ring at the bridge between the mother and bud cells. What regulates the assembly and function of septins however has remained obscure. All septins share a highly conserved domain related to those found in small GTPases and septins have been shown to bind and hydrolyze GTP although the properties of this domain and the relationship between polymerization and GTP binding hydrolysis is unclear. Here we show that human septin 2 is phosphorylated in vivo at Ser218 by casein kinase II. In addition we show that recombinant septin 2 binds guanine nucleotides with a Kd of pM for GTPyS and pM for GDP. It has a slow exchange rate of 7 X 10-5 s-1 for GTPyS and 5 X 10-4 s-1 for GDP and an apparent kcat value of X 10-4 s-1 similar to those of the Ras superfamily of GTPases. Interestingly the nucleotide binding affinity appears to be altered by phosphorylation at Ser218. Finally we show that a single septin protein can form homotypic filaments in vitro whether bound to GDP or GTP. Septins are a family of highly .

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