Tubulins are a superfamily of actually at least five members:
a- and b-tubulin, the main components of microtubules, g-tubulin
, that is part of the MTOCs , and d- and e-tubulin  with
yet unknown function. Each tubulin may exist in several isotypes
. Most isotypes may be posttranslationally modified. The most
common modification is the detyrosination of a-tubulin by
carboxypeptidase and tyrosination by tubulin-tyrosine-ligase .
Detyrosination of a-tubulin is commonly a marker for stable
Recently, Linder et al.  identified and sequenced the genes for tubulin expression in Reticulomyxa. They found two isoforms of a-tubulin with a calculated molecular weight of 49,7 kD and two forms of b-tubulin with 52,5 and 49,6 kD. We localized the a- and one of the b-tubulins on 2D-PAGES of Reticulomyxa extracts and confirmed the calculated weights by means of IR-MALDI-TOF Mass-Spectrometry of blotted proteins. We also found a new a-tubulin isoform with a molecular weight of only approximately 45kD. Monoclonal antibodies in western blot do not cross-react between the different a-tubulin-isoforms, so we conclude, that they share only few common epitopes.
When evaluating the tyrosination/detyrosination state of the different a-tubulins, we found, that the 49,7 kD a-tubulins described by Linder do not react with any of the tyr- or glu-tubulin specific antibodies in western blot, but bind to the 20C6 anti-tyr-tubulin mAb in immunfluorescence. The 45 kD a-tubulin reacts with both, 27C2 anti-tyr-tubulin and ID5 anti-glu-tubulin mAb in a competitive manner. Therefore we conclude, that the 45 kD a-tubulin of Reticulomyxa is one of the most aberrant tubulins yet characterized, and further on, that "there is not necessarily everything tyr-tubulin, that reacts with an anti-tyr-tubulin antibody".
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