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Cation selective promotion of tubulin polymerization by alkali metal chlorides
Author(s) -
Wolff J.,
Sackett Dan L.,
Knipling Leslie
Publication year - 1996
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560051008
Subject(s) - chemistry , polymerization , tubulin , monomer , polymer chemistry , dimer , microtubule , depolymerization , polymer , photochemistry , stereochemistry , organic chemistry , biology , microbiology and biotechnology
Abstract A role for charge‐based interactions in protein stability at the monomer or dimer level is well known. We show here that such interactions can also be important for the higher‐order structures of microtubule assembly. Alkali metal chlorides increase the rate of polymerization of pure tubulin driven by either taxol or dimethyl sulfoxide. The effect is cation selective, exhibiting a sequence Na + > K + > Li + > Cs + , with optimal concentrations for Na + at ∽ 160 mM. Hofmeister anion effects are additive with these rate stimulations. Sodium is less potent than guanidinium ion stimulation reported previously, but produces a larger fraction of normal microtubules. Alkali metal cations lower the critical concentration by a factor of ∽2, produce cold reversible polymers whose formation is sensitive to podophyllotoxin inhibition, increase the fraction of polymers present as microtubules from ∽0.9 to 0.99, and reverse or prevent urea‐induced depolymerization of microtubules. In the presence of microtubule‐associated proteins, the promotion of polymerization is no longer cation selective. In the polymerization of tubulin S, in which the acidic C termini of both monomers have been cleaved, the cation enhancement is markedly decreased, although selectivity persists. Because the selectivity sequence is similar to that of the coil/helix transition of polyglutamic acid, we suggest that a major part, although not all, of the cation selective enhancement of polymerization results from shielding of the glutamate‐rich C termini of the tubulin monomers.