Chlamydomonas cilia proteins

Axonemal dyneins are highly complex molecular motors that power ciliary
motility. These multi-subunit enzymes are assembled at dedicated sites
within the cytoplasm. At least nineteen cytosolic factors are specifically
needed for the generation of dynein holoenzymes and/or their trafficking
to the growing cilium. Many proteins are subject to N-terminal processing
and acetylation which can generate degrons subject to the AcN-end rule and
alter N-terminal electrostatics, generate new binding interfaces, and
affect subunit stoichiometry through targeted degradation. Here we have
used mass spectrometry of cilia samples and electrophoretically purified
dynein heavy chains from Chlamydomonas to define their N-terminal
processing; we also detail the N-terminal acetylase complexes present in
this organism. We identify four classes of dynein heavy chain based on
their processing pathways by two distinct acetylases one of which is
dependent on methionine aminopeptidase activity. In addition, we find that
one component of both the outer dynein arm intermediate/light chain
subcomplex and the docking complex are processed to yield an unmodified
Pro residue which may provide a setpoint to direct the cytosolic
stoichiometry of other dynein complex subunits that contain N-terminal
degrons. Thus, we identify an additional level of processing and
complexity in the pathways leading to axonemal dynein formation in
cytoplasm.