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GTP binding and hydrolysis kinetics of human septin 2
Author(s) -
Huang YiWei,
Surka Mark C.,
Reynaud Denis,
PaceAsciak Cecil,
Trimble William S.
Publication year - 2006
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2006.05333.x
Subject(s) - septin , gtpase , gtp' , ras superfamily , cytokinesis , guanine nucleotide exchange factor , biology , biochemistry , microbiology and biotechnology , phosphorylation , nucleotide , gtp binding protein regulators , g protein , cell division , signal transduction , enzyme , cell , gene
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 K d of 0.28 µ m for GTPγS and 1.75 µ m for GDP. It has a slow exchange rate of 7 × 10 −5 s −1 for GTPγS and 5 × 10 −4 s −1 for GDP, and an apparent k cat value of 2.7 × 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.