Centrioles and cilia are microtubule-based structures, whose precise formation requires controlled cytoplasmic tubulin incorporation. How cytoplasmic tubulin is recognized for centriolar/ciliary-microtubule construction remains poorly understood. Centrosomal-P4.1-associated-protein (CPAP) binds tubulin via its PN2-3 domain. Here, we show that a C-terminal loop-helix in PN2-3 targets β-tubulin at the microtubule outer surface, while an N-terminal helical motif caps microtubule's α-β surface of β-tubulin. Through this, PN2-3 forms a high-affinity complex with GTP-tubulin, crucial for defining numbers and lengths of centriolar/ciliary-microtubules. Surprisingly, two distinct mutations in PN2-3 exhibit opposite effects on centriolar/ciliary-microtubule lengths. CPAPF375A, with strongly reduced tubulin interaction, causes shorter centrioles and cilia exhibiting doublet- instead of triplet-microtubules. CPAPEE343RR that unmasks the β-tubulin polymerization surface displays slightly reduced tubulin-binding affinity inducing over-elongation of newly forming centriolar/ciliary-microtubules by enhanced dynamic release of its bound tubulin. Thus CPAP regulates delivery of its bound-tubulin to define the size of microtubule-based cellular structures using a ‘clutch-like' mechanism.

Histone recognition constitutes a key epigenetic mechanism in gene regulation and cell fate decision. PHF14 is a conserved multi-PHD finger protein that has been implicated in organ development, tissue homeostasis, and tumorigenesis. Here we show that PHF14 reads unmodified histone H3(1–34) through an integrated PHD1-ZnK-PHD2 cassette (PHF14PZP). Our binding, structural and HDX-MS analyses revealed a feature of bipartite recognition, in which PHF14PZP utilizes two distinct surfaces for concurrent yet separable engagement of segments H3-Nter (e.g. 1–15) and H3-middle (e.g. 14–34) of H3(1–34). Structural studies revealed a novel histone H3 binding mode by PHD1 of PHF14PZP, in which a PHF14-unique insertion loop but not the core β-strands of a PHD finger dominates H3K4 readout. Binding studies showed that H3-PHF14PZP engagement is sensitive to modifications occurring to H3 R2, T3, K4, R8 and K23 but not K9 and K27, suggesting multiple layers of modification switch. Collectively, our work calls attention to PHF14 as a ‘ground’ state (unmodified) H3(1–34) reader that can be negatively regulated by active marks, thus providing molecular insights into a repressive function of PHF14 and its derepression.

Schizophrenia (SZ) is a psychiatric disorder with complex genetic risk dictated by interactions between hundreds of risk variants. Epigenetic factors, such as histone posttranslational modifications (PTMs), have been shown to play critical roles in many neurodevelopmental processes, and when perturbed may also contribute to the precipitation of disease. Here, we apply an unbiased proteomics approach to evaluate combinatorial histone PTMs in human induced pluripotent stem cell (hiPSC)-derived forebrain neurons from individuals with SZ. We observe hyperacetylation of H2A.Z and H4 in neurons derived from SZ cases, results that were confirmed in postmortem human brain. We demonstrate that the bromodomain and extraterminal (BET) protein, BRD4, is a bona fide ‘reader’ of H2A.Z acetylation, and further provide evidence that BET family protein inhibition ameliorates transcriptional abnormalities in patient-derived neurons. Thus, treatments aimed at alleviating BET protein interactions with hyperacetylated histones may aid in the prevention or treatment of SZ.