POSTTRANSLATIONAL MODIFICATIONS IN THE C-TERMINAL TAIL OF AXONEMAL TUBULIN FROM SEA-URCHIN SPERM

After proteolytic digestion of sperm tubulin from sea urchin Paracentr otus lividus, C-terminal peptides were isolated by chromatographic sep arations. The peptides mere analyzed by Edman degradation and matrix-a ssisted laser desorption/ionization-time of flight mass spectrometry. About 70% of the isolated C-terminal peptides were unmodified. The rem aining modified peptides have undergone a combination of numerous post translational modifications generating significant heterogeneity of sp erm tubulin, alpha-Tubulin is modified by detyrosylation, release of t he penultimate glutamate, polyglutamylation, and polyglycylation. Glyc ylation and glutamylation can coexist within one alpha-tubulin isoform , beta-Tubulin undergoes polyglycylation but was not observed to be po lyglutamylated. The number of units posttranslationally added reaches 11 and 12 glycyl units on beta- and alpha-tubulin, respectively. This is different from the polyglycylation of axonemal tubulin in Parameciu m cilia where up to 40 added glycyl units were observed both on alpha- and beta-tubulin.