Novel revertants of Chlamydomonas vfl2 suggest a role for a flexible central α-helical region in centrin function in flagellar basal bodies.

A Chlamydomonas mutant, vfl2 , displays aberrant flagellar numbers due to an E101K mutation in the centrin gene. We isolated 21 revertants-12 intragenic and 9 extragenic-that suppress the mutant's abnormal phenotype. AlphaFold2 modeling indicates that the wild-type, mutant, and revertant proteins are structurally similar. However, the vfl2 mutant centrin forms three salt bridges in the central region of the core α-helix, whereas the wild type and all intragenic revertants have only two salt bridges or disrupted helix continuity. These results indicate that flexibility of the central helix, maintained by limited electrostatic interactions, is important for proper centrin function.