Crystal structure of human PACRG in complex with MEIG1

Abstract

In human, the Parkin Co-Regulated Gene (PACRG) shares a bidirectional promoter with Parkin, a gene involved in Parkinson's disease, mitochondrial quality control and inflammation. The PACRG protein is essential to the formation of the inner junction between doublet microtubules of the axoneme, a structure found in flagella and cilia. PACRG interacts with tubulin as well as the meiosis expressed gene 1 (MEIG1) protein, which is essential for spermiogenesis in mice.However, the 3D structure of human PACRG is unknown. Here, we report the crystal structure of the C-terminal domain of human PACRG in complex with MEIG1 at 2.1 Å resolution. PACRG adopts an a-helical structure with a loop insertion that mediates a conserved network of interactions with MEIG1. Using the cryo-electron tomography structure of the axonemal doublet microtubule from the flagellated protozoan Chlamydomonas reinhardtii, we generate a model of a mammalian microtubule doublet inner junction, which reveals how PACRG interacts with tubulin subunits in both the A-and B-tubules. Furthermore, the model shows that MEIG1 interacts with btubulin on the outer surface of the B-tubule, facing towards the central pair of the axoneme. We also model the PACRG-like protein (PACRGL), a homolog of PACRG with potential roles in microtubule remodelling and axonemal inner junction formation. Finally, we explore the evolution of the PACRG and Parkin head-to-head gene structure and analyze the tissue distribution of their transcripts. Our work establishes a framework to assess the function of the PACRG family of proteins and its adaptor proteins in the function of motile and non-motile cilia.We thank K. Winklhofer and J. Menschede for useful discussion that contributed to the development of this study. The beamline 08ID-1 at the Canadian

The inner junction complex of the cilia is an interaction hub that involves tubulin post-translational modifications

“…2D), while FAP20 seems to have minimal to no contact with the lateral side. Recent work shows that human PACRG-MEIG1 complex can prevent tubulin sheet closure, supporting the lateral interaction of PACRG (31). This infers that the transport of FAP20 and PACRG to the right position during assembly must be regulated.…”

“…To facilitate a successful IJ assembly, chaperones might be needed for the transport of PACRG and FAP20. PACRG forms a complex with MEIG1 (31). Even though MEIG1 is not present in lower eukaryotes and that the MEIG1 binding loop is not conserved between Chlamydomonas and humans, a chaperone similar to MEIG1 can function to target PACRG to the lateral interface of the PF B10.…”

“…A partial homology model of C. reinhardtii PACRG (B1B601) was constructed using the crystal structure of the human homolog (Q96M98-1) as template (31). The model was completed by building segments N2-D148 and Y249-L270 de novo in density using Coot v0.8.9.1 (52).…”