Biology subjects

Bui, K. H.

Publications and source records attributed to Bui, K. H..

22 records · Page 2Linked to original sources

bioRxiv2019

Crystal structure of human PACRG in complex with MEIG1

In human, the Parkin Co-Regulated Gene (PACRG) shares a bidirectional promoter with Parkin, a gene involved in Parkinsons 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 [A] resolution. PACRG adopts an -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 {beta}-tubulin 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.

cell biology↗

bioRxiv2019

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

Microtubules are cytoskeletal structures involved in structural support, microtubule-based transport and the organization of organelles in the cells. The building blocks of the microtubule, the - and {beta}-tubulin heterodimers, polymerize into protofilaments, that associate laterally to form the hollow microtubule. There exists a specific type of microtubule structures in the cilia, termed doublet microtubules, where high stability is required for ciliary beating and function. The doublet microtubule, consisting of a complete A-tubule and a partial B-tubule maintains its stability through unique interactions at its outer and inner junctions, where the A- and B-tubules meet.\n\nUsing cryo-electron microscopy, we present the answer to the long-standing question regarding the identities, localizations and structures of the Chlamydomonas doublet microtubule inner junction proteins. Using a combination of sequence bioinformatics and mass spectrometry, we identified two new inner junction proteins, FAP276 and FAP106, and an inner junction associated protein FAP126. We show that inner junction proteins PACRG and FAP20, together with FAP52, previously unidentified FAP276, FAP106 and FAP126, form an interaction hub at the inner junction, which involves tubulin sites for post-translational modifications. We further compare the Chlamydomonas and Tetrahymena doublet microtubule structures to understand the common and species-specific features of the inner junction.

biophysics↗

bioRxiv2019

Identification and mapping of central pair proteins by proteomic analysis

Cilia or flagella of eukaryotes are small micro-hair like structures that are indispensable to single-cell motility and play an important role in mammalian biological processes. Cilia or flagella are composed of nine doublet microtubules surrounding a pair of singlet microtubules called the central pair (CP). Together, this arrangement forms the canonical and highly conserved 9+2 axonemal structure. The CP, which is a unique structure exclusive to motile cilia, is a pair of structurally dimorphic singlet microtubules decorated with numerous associated proteins. Mutations of CP-associated proteins cause several different physical symptoms termed ciliopathies. Thus, it is crucial to understand the architecture of the CP. However, the protein composition of the CP was poorly understood. This was because identification of CP proteins was mostly limited by available Chlamydomonas mutants of CP proteins. In this study, we conducted a comprehensive CP proteome analysis using several CP mutants and identified 37 novel CP protein candidates. By using Chlamydomonas strains lacking specific CP sub-structures, we also present a more complete model of localization of known and newly identified CP proteins. This work has established a new foundation for CP protein analysis for future studies.

biophysics↗

bioRxiv2019

Tubulin Lattice in Cilia is in a Stressed Form Regulated by Microtubule Inner Proteins

Cilia, the hair-like protrusions that beat at high frequencies to propel a cell or move fluid around the cell, are composed of radially bundled doublet microtubules. The doublet microtubule is composed of a 13-protofilament A-tubule, a partial 10-protofilament B-tubule and microtubule inner proteins (MIPs) inside the tubulin lattice. In this study, we present the near-atomic resolution map of the Tetrahymena doublet microtubules. The map demonstrates that the network of microtubule inner proteins is weaving into the tubulin lattice, forming an inner sheath of proteins. In addition, we also obtain the tubulin lattice structure with missing MIPs by Sarkosyl treatment. In this structure, the tubulin lattice showed significant longitudinal compaction and lateral angle changes between protofilaments. These results are evidence that the binding of MIPs directly affects and stabilizes the tubulin lattice. It is also suggested that the doublet microtubule is an intrinsically stressed filament and this stress could be exploited in the regulation of ciliary waveforms.

biophysics↗