Assembly of Atlantic Cod ( Gadus morhua) Brain Microtubules at Different Temperatures: Dependency of Microtubule-Associated Proteins Is Relative to Temperature

Abstract

Isolated cod ( Gadus morhua) brain microtubules were found to have a broad temperature interval for assembly. In contrast to mammalian microtubules they assembled even at as low temperatures as 14°C. Evidence was found that temperature alters the dependency of microtubule-associated proteins (MAPs) for assembly. The assembly was MAPs-dependent at low, but not at higher temperatures. Assembly at +18°C was inhibited by both NaCl and estramustine phosphate. These compounds are well known to inhibit the binding of MAPs to tubulin. At higher temperatures there was no MAPs dependency for assembly, despite that MAPs bound to the microtubules. Cow MAPs had the same effect as cod MAPs, suggesting that despite differences in MAP composition, the effect is not caused by the unusual composition of cod MAPs. The results therefore suggest that these differences in MAPs dependency are due to intrinsic properties of cod tubulin or iubulin-to-tubulin interactions. Small temperature-induced conformational changes of tubulin and a slight enrichment of acetylated and detyrosinated tubulin in microtubules assembled at +30°C as compared to +15°C, were observed. The ability to alter the assembly stimulating effect of MAPs may be important for the cell to regulate microtubule dynamics and stability. In addition, changes in tubulin conformation and composition of tubulin isoforms may reflect adaptations for microtubule assembly at low temperatures.