Fig. 2: Actin isoforms and tubulin isotypes in humans.

a,b A summary of the six human actin isoforms (a) and nine α-tubulin and nine β-tubulin isotypes (b). In a, the N-terminal sequences of actin isoforms are displayed, with sequence differences highlighted in pink. The gray regions at the N terminus indicate segments that are proteolytically removed and subsequently acetylated. In the case of β-actin, the processed N-terminus can also be arginylated. In b the N-terminal sequences of α-tubulin and β-tubulin isotypes are highly conserved, except for tubulin α4B, which shows some divergence. Sequence variations are highlighted in pink. Notably, the MREC motif (green) in α-tubulin and the MREI motif (blue) in β-tubulin are highly conserved across isotypes; these motifs are essential for autoregulation as they mediate interaction with TTC5 (Fig. 3). c Diversity of C-terminal tails and PTMs in human tubulin isotypes. Amino acids are color-coded according to their biochemical properties. Experimentally validated polyglutamylation sites are highlighted in bold, while all glutamate residues are shown as potential modification sites. Documented C-terminal truncations of α-tubulins are marked with ‘▼’.