Colchicine‐binding sites of brain tubulins from an Antarctic fish and from a mammal are functionally similar, but not identical: Implications for microtubule assembly at low temperature

• Published in: Cell Motility and the Cytoskeleton
• Main Authors: Skoufias, Dimitrios A., Wilson, Leslie, Detrich, H. William
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1992
• Subjects: Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1002/cm.970210403; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fcm.970210403; https://onlinelibrary.wiley.com/doi/pdf/10.1002/cm.970210403

Abstract The tubulins of Antarctic fishes possess adaptations that favor microtubule for mation at low body temperatures (Detrich et al.: Biochemistry 28:10085–10093, 1989). To determine whether some of these adaptations may be present in a domain of tubulin that participates directly or indirectly in lateral contact between microtubule protofilaments, we have examined the energetics of the binding of colchicine, a drug thought to bind to such a site, to pure brain tubulins from an Antarctic fish (Notothenia gibberifrons) and from a mammal (the cow, Bos taurus) , At temperatures between 0 and 20 0 C, the affinity constants for colchicine binding to the fish tubulin were slightly smaller (1.5–2.6‐fold) than those for bovine tubulin. van't Hoff analysis showed that the standard enthalpy changes for colchicine binding to the two tubulins were comparable (δH° = + 10.6 and + 7.4 kcal mol‐ 1 for piscine and bovine tubulins, respectively), as were the standard entropy changes (δS° = +61.3 eu for N. gibberifrons tubulin, +51.2 eu for bovine tubulin). At saturating concentrations of the ligand, the maximal binding stoichiometry for each tubulin was ∼ 1 mol colchicine/mol tubulin dimer. The data indicate that the colchicine‐binding sites of the two tubulins are similar, but probably not identical, in structure. The apparent absence of major structural modifications at the colchicine site suggests that this region of tubulin is not involved in functional adaptation for low‐temperature polymerization. Rather, the colchicine site of tubulin may have been conserved evolutionarily to serve in vivo as a receptor for endogenous molecules (i.e., “colchicine‐like” molecules or MAPs) that regulate microtubule assembly.