title: The axonemal microtubules of the Chlamydomonas flagellum differ in tubulin isoform content.
abstract: Little is known of the molecular basis for the diversity of microtubule structure and function found within the eukaryotic flagellum. Antibodies that discriminate between tyrosinated alpha tubulin and post-translationally detyrosinated alpha tubulin were used to localize these complementary tubulin isoforms in flagella of the single-celled green alga Chlamydomonas reinhardtii. Immunofluorescence analysis of intact axonemes detected both isoforms along most of the lengths of flagella; however, each had a short distal zone rich in tyrosinated tubulin. Localizations on splayed axonemes revealed that the microtubules of the central-pair apparatus were rich in tyrosinated tubulin, while outer doublets contained a mixture of both isoforms. Immunoelectron analysis of individual outer doublets revealed that while tyrosinated tubulin was present in both A and B tubules, detyrosinated tubulin was largely confined to the wall of the B hemi-tubules. The absence of detyrosinated tubulin from the A tubules of the outer doublets and the microtubules of the central pair, both of which extend past the B hemi-tubules of the outer doublets in the flagellar tip, explained the appearance of a tyrosinated tubulin-rich distal zone on intact axonemes. Localizations performed on cells regenerating flagella revealed that flagellar assembly used tyrosinated tubulin; detyrosination of the B tubule occurred during later stages of regeneration, well after microtubule polymerization. The developmental timing of detyrosination, which occurs over a period during which the regrowing flagella begin to beat more effectively, suggests that post-translational modification of the B tubule surface may enhance dynein/B tubule interactions that power flagellar beating.
authors.affiliation: Department of Biology, Haverford College, Haverford, PA 19041, USA. kjohnson@haverford.edu
authors.forename: K A
authors.initials: KA
authors.lastname: Johnson
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000378:metabolism* / Q000648:ultrastructure; D005407:Flagella / Q000378:metabolism* / Q000648:ultrastructure; D007536:Isomerism; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D019000:Phosphotyrosine / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D014404:Tubulin; D019000:Phosphotyrosine; D014443:Tyrosine