Protein adaptation to low temperatures: a comparative study of alpha-tubulin sequences in mesophilic and psychrophilic algae

The alpha-tubulin genes from two psychrophilic algae belonging to the genus Chloromonas (here named ANT1 and ANT3) have been isolated and sequenced. T he genes anti and ant3 contain 4 and 2 introns, respectively. The coding DN A sequences are 90% identical but the degree of isology is very high at the polypeptide level (more than 97% strict identities). The ANT1 and ANT3 alp ha-tubulin amino acid sequences were compared to the corresponding sequence of the mesophilic alga Chlamydomonas reinhardtii. Of the 15 substitutions detected in ANT1 and/or ANT3, 5 are common to both psychrophilic algae. The recorded substitutions have been analyzed in terms of cold adaptation on t he basis of the available three-dimensional structure of the alpha,beta-tub ulin heterodimer from pig brain, Most of these are subtle changes, but two substitutions, M268V and A295V occurring in the region of interdimer contac ts, could be of great significance for the cold stability of Antarctic alga e microtubules due to the fact that the entropic control of microtubule ass embly is particularly high in cold adaptes species.