A Novel Tctex2-related Light Chain Is Required for Stability of Inner Dynein Arm I1 and Motor Function in the Chlamydomonas Flagellum

Linda M Dibella,Elizabeth F Smith,Ramila S Patel-King,Ken-Ichi Wakabayashi,Stephen M King

doi:10.1074/jbc.m313540200

Linda M Dibella, Elizabeth F Smith + Show 3 more

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https://doi.org/10.1074/jbc.m313540200

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Abstract

Tctex1 and Tctex2 were originally described in mice as putative distorters/sterility factors involved in the non-Mendelian transmission of t haplotypes. Subsequently, these proteins were found to be light chains of both cytoplasmic and axonemal dyneins. We have now identified a novel Tctex2-related protein (Tctex2b) within the Chlamydomonas flagellum. Tctex2b copurifies with inner arm I1 after both sucrose gradient centrifugation and anion exchange chromatography. Unlike the Tctex2 homologue within the outer dynein arm, analysis of a Tctex2b-null strain indicates that this protein is not essential for assembly of inner arm I1. However, a lack of Tctex2b results in an unstable dynein particle that disassembles after high salt extraction from the axoneme. Cells lacking Tctex2b swim more slowly than wild type and exhibit a reduced flagellar beat frequency. Furthermore, using a microtubule sliding assay we observed that dynein motor function is reduced in vitro. These data indicate that Tctex2b is required for the stability of inner dynein arm I1 and wild-type axonemal dynein function.

Highlights

Tctex1 and Tctex2 were originally described in mice as putative distorters/sterility factors involved in the non-Mendelian transmission of t haplotypes
Tctex2b Defines a New Subfamily of Dynein LCs—To date, three members of the Tctex1/Tctex2 family have been identified in Chlamydomonas; they are Tctex1, an inner arm I1 subunit [13] that functions as a component of cytoplasmic dynein [22], LC2 [24], an outer arm LC that is required for assembly of that dynein [28], and Tctex2b, which is described here
We have shown that in Chlamydomonas Tctex2b is encoded by a single gene and that its message is up-regulated in response to deflagellation, suggesting that it functions in the flagellum

Summary

Introduction

Tctex and Tctex were originally described in mice as putative distorters/sterility factors involved in the non-Mendelian transmission of t haplotypes. Unlike the Tctex homologue within the outer dynein arm, analysis of a Tctex2b-null strain indicates that this protein is not essential for assembly of inner arm I1. Using a microtubule sliding assay we observed that dynein motor function is reduced in vitro These data indicate that Tctex2b is required for the stability of inner dynein arm I1 and wild-type axonemal dynein function. Within flagella of the unicellular green alga Chlamydomonas, the apparently homogeneous ϳ2-MDa outer arms are assembled at 24-nm intervals along the length of the A tubules of the outer doublet microtubules This motor complex helps define the beat frequency of the flagellum and provides ϳ4⁄5 of the power output [3, 4]. LC2 is a Tctex homologue [24] that is essential for the assembly of the Chlamydomonas outer dynein arm within the flagellar axoneme [28]

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