Protein adaptation in polar environments: a comparative study of α-tubulin sequences in mesophilic and psychrophilic polar microalgae

Abstract

Microtubules assemble by polymerization of tubulin dimers and their stability is temperature dependent. Under low temperature conditions, microtubules disassemble because the polymerization of tubulin dimer is disturbed and it hinders the overall development of organisms. It is suggested that therefore, organisms living in a cold environment have evolved to overcome this obstacle of microtubule disassembly by amino acid substitution in tubulin. We aimed to investigate whether amino acid substitution in tubulin is common phenomenon occurring in polar microalgae and is responsible for their successful growth at freezing temperature. The full-length cDNAs of α-tubulin from eight genera with 14 microalgal strains (ArF0004, ArF0008, ArF0013, ArF0024, ArF0025, ArF0026, ArF0027, ArF0028, ArF0029, ArF0032, AnF0048, AnM0008, AnM0030, and AnM0045) which were collected from the Arctic and the Antarctica were obtained by 3'- and 5'- race analyses. We compared amino acid sequences of them with that of α-tubulin from mesophilic alga, Chlamydomonas reinhardtii and found several amino acid substitutions in tubulins of most polar microalgae. Among substitutions, the A295V region was previously reported to play an important role in the producing protofilament by increasing hydrophobicity. 10 out of 14 microalgal strains (72%) showed a substitution of alanine (A) to valine (V) in the 295th residue, de