Effect of sodium chloride on the structure of tubulin assemblies

By use of a taxol-containing assembly medium, it has been demonstrated that the mean protofilament number of microtubule populations is significantly lower at elevated NaCl concentrations. Assembly of microtubule protein, i.e. tubulin plus microtubule-associated proteins (MAPs), at 80 and 580 mM NaCl results in microtubule populations with mainly 13 and 10 protofilaments whereas microtubules formed from tubulin alone have 12 and 10 protofilaments, respectively. Moreover, when MAPs are prevented from assembly, the formation of taxol-induced aberrant assemblies (C- and S-shaped protofilament ribbons) is suppressed at high NaCl concentrations in favour of microtubules. The described effects are obviously caused by both weakening of MAP binding to tubulin and alterations in tubulin-tubulin association.