Polyglycylation of tubulin in the diplomonad Giardia lamblia, one of the oldest eukaryotes

Abstract
We have searched for post‐translational modifications in tubulin of the diplomonad Giardia lamblia, which is a representative of the earliest branches in eukaryotic evolution. The carboxyterminal peptide of α‐tubulin was isolated and characterized by automated sequencing and mass spectrometry. Some 60% of the peptide is unmodified, while the remainder shows various degrees of polyglycylation. The number of glycyl residues in the lateral side chain ranges from 2 to 23. All peptide species encountered end with alanine‐tyrosine, indicating the absence of a detyrosination/tyrosination cycle. We conclude that tubulin‐specific polyglycylation could be as old as tubulin and axonemal structures.