WDR47 and Camsap are involved in the molecular mechanisms that regulate the formation of central microtubules in kinesciliae

Kinesilia are microtubule-based accessory structures on the surface of eukaryotic cells, which are widely distributed
in tissues and organs such as trachea, ventricles and fallopian tubes.
Through periodic and rapid oscillations, the cilia can help clear the airways, drive cerebrospinal fluid circulation, and facilitate the movement of the fertilized egg towards the uterus
.
Defects in the cilia can cause abnormal development or function of multiple organs such as the brain and kidneys, causing a variety of ciliary diseases
such as chronic sinusitis, recurrent respiratory infections, infertility and hydrocephalus.

From the structural point of view, the moving cilia are composed of a base, axons and a cilia membrane, and their axon structure is in a "9+2" mode, that is, it is composed
of 9 groups of microtubule duplets and two central microtubules surrounded by a central sheath.
The structure of the moving cilia begins in the matrix at the base of the cilia in the cytoplasm
.
The 9 groups of microtubule triplets of the basal body extend extracellularly, forming 9 groups of microtubule
triplets around the periphery of cilia.
The central microtubule is not attached to the matrix, and there is no clear answer
to the formation mechanism of the central microtubule.

WDR47 and Camsap are identified central microtubule regulatory proteins
.
It was found that Wdr47 directly interacted with the microtubule-binding protein Camsap and enriched it to the negative end of the central microtubule to ensure the correct formation
of the central microtubule.
However, the molecular mechanism of the interaction between Wdr47 and Camsap is unclear
.
The research group of Feng Wei of the Institute of Biophysics of the Chinese Academy of Sciences and the research group of Zhu Xueliang of the Center for Excellence in Molecular Cell Science of the Chinese Academy of Sciences have carried out cooperative research on this scientific problem, and through structural biology, biochemistry and cell biology research, the molecular mechanism
by which Wdr47 recognizes the Camsap family protein and recruits it into the central sheath to regulate the formation of central microtubules is revealed 。 The study is currently published in the journal Cell Reports under the title "Intertwined Wdr47-NTD dimer recognizes a basic-helical motif in Camsap proteins for proper central-pair microtubule formation
.
"

This study first studied the interaction site between Wdr47 and Camsap3 protein, and finally determined that the NTD domain (Wdr47-NTD) of Wdr47 had a direct interaction
with a disordered region rich in basic amino acids in Camsap3 by biochemical means.
Through sequence analysis, this sequence was found to be very conserved in the entire Camsap family of proteins and was named Wdr47 binding motif (WBR-motif).

Subsequently, the structure
of Wdr47-NTD and Wdr47-NTD/Camsap3-WBR-motif complexes was resolved by X-ray crystallography 。 Structural analysis found that Wdr47-NTD formed an intertwined dimer; In the complex, the WBR-motif of Camsap3 forms a short helix structure at the beginning of the helix directly inserted into a hydrophobic pocket in the intertwined region of Wdr47-NTD, which is surrounded by acidic amino acids that happen to form a charge complement
to the basic amino acids in WBR-motif.
Previous studies have found that in mouse ependymal cells knocked out by Wdr47, the central microtubule of the moving cilia is missing and accompanied by abnormal cilia
swinging.
In this Wdr47-deficient cell, transfection of wild-type Wdr47 can play a good rescue effect, but transfection of Wdr47-F260A mutant that destroys Wdr47-Camsap interaction is not significant
.
In summary, the study reveals the molecular mechanism of Wdr47 and Camsap interaction and its important role
in the formation of microtubules in the central microtubule of the moving cilia.

Schematic diagram of the molecular mechanism by which WDR47 recognizes Camsap and its involvement in regulating the formation of central microtubules in kinesicilia

Professor Feng Wei from the Institute of Biophysics, Chinese Academy of Sciences, and Professor Zhu Xueliang from the Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences are the corresponding authors
of this paper.
Dr.
Ren Jinqi in Feng Wei's research group, Li Dong, doctoral student Li Dong, and doctoral student Liu Juyuan in Zhu Xueliang's research group, are the co-first authors
of this paper.
This project has been supported
by the National Key Research and Development Program, the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences (B), and the National Natural Science Foundation of China.

Article link: https://doi.
org/10.
1016/j.
celrep.
2022.
111589

(Contributed by: Feng Wei Research Group)