Biology subjects

Sekulic, N.

Publications and source records attributed to Sekulic, N..

5 recordsLinked to original sources

bioRxiv2025

Solution conformational differences between conventional and CENP-A nucleosomes are accentuated by reversible deformation under high pressure

Solution-based interrogation of the physical nature of nucleosomes has its roots in X-ray and neutron scattering experiments, including those that provided the initial observation that DNA wraps around core histones. In this study, we performed a comprehensive small-angle scattering study to compare canonical nucleosomes with variant centromeric nucleosomes harboring the histone variant, CENP-A. We used nucleosome core particles (NCPs) assembled on an artificial positioning sequence (Widom 601) and compared these to those assembled on a natural -satellite DNA cloned from human centromeres. We establish the native solution properties of octameric H3 and CENP-A NCPs using analytical ultracentrifugation (AUC), small-angle X-ray scattering (SAXS), and contrast variation small-angle neutron scattering (CV-SANS). Using high-pressure SAXS (HP-SAXS), we discovered that both histone identity and DNA sequence have an impact on the stability of octameric nucleosomes in solution under high pressure (300 MPa), with evidence of reversible unwrapping in these experimental conditions. Both canonical nucleosomes harboring conventional histone H3 and their centromeric counterparts harboring CENP-A have a substantial increase in their radius of gyration, but this increase is much less prominent for centromeric nucleosomes. More broadly for chromosome-related research, we note that as HP-SAXS methodologies expand in their utility, we anticipate this will provide a powerful solution-based approach to study nucleosomes and higher-order chromatin complexes.

biophysics↗

bioRxiv2025

Non-nucleosomal (CENP-A/H4)2 - DNA complexes as a possible platform for centromere organization

The centromere is a part of the chromosome that is essential for the even segregation of duplicated chromosomes during cell division. It is epigenetically defined by the presence of the histone H3 variant CENP-A. CENP-A associates specifically with a group of 16 proteins that form the centromere-associated network of proteins (CCAN). In mitosis, the kinetochore forms on the CCAN to connect the duplicated chromosomes to the microtubules protruding from the cell poles. Previous studies have shown that CENP-A replaces H3 in nucleosomes, and recently the structures of CENP-A-containing nucleosomes in complex with CCANs have been revealed, but they show only a limited interaction between CCANs and CENP-A. Here, we report the cryoEM structure of 2x(CENP-A/H4)2-di-tetramers assembled on DNA in the absence of H2A/H2B histone dimer and speculate how (CENP-A/H4)2-tetramers and -di-tetramers might serve as a platform for CCAN organization. Main pointsO_LICENP-A/H4 in the absence of H2A/H2B dimers associate on DNA to form di-tetrasomes C_LIO_LICENP-A/H4 di-tetrasomes are stable but highly flexible structures resembling nucleosomes C_LIO_LICENP-A/H4 tetrasomes bind CENP-N/L and can serve as platform for centromere organisation C_LI

biochemistry↗

bioRxiv2024

Insects evolved a monomeric histone-fold domain in the CENP-T protein family

The histone fold domain (HFD) is a conserved protein interaction module that requires stabilization through a handshake interaction with an HFD partner. All HFD proteins known to date form obligate dimers to shield the extensive hydrophobic residues along the HFD. Here, we find that the lepidopteran kinetochore protein CENP-T is soluble as a monomer. We attribute this stability to a structural rearrangement, which leads to the repositioning of the HFD helix 3. This brings a conserved two-helical extension closer to the histone fold, where it takes over the position and function of the CENP-T partner CENP-W. This change has no effect on the DNA binding ability of the lepidopteran CENP-T. Our analysis suggests that the monomeric HFD originated in the last common ancestor of insects, with a possible second independent origin in acariformes, both of which lack CENP-W. Our study highlights an unexpected structural variation in a protein module as conserved and optimized as the HFD providing a unique perspective on the evolution of protein structure and the forces driving it.

cell biology↗

bioRxiv2022

The structural basis of the multi-step allosteric activation of Aurora B kinase

Aurora B, together with IN-box, the C-terminal part of INCENP, forms an enzymatic complex that ensures faithful cell division. The [Aurora B/IN-box] complex is activated by autophosphorylation in the Aurora B activation loop and in IN-box, but it is not clear how these phosphorylations activate the enzyme. We used a combination of experimental and computational studies to investigate the effects of phosphorylation on the molecular dynamics and structure of [Aurora B/IN-box]. In addition, we generated partially phosphorylated intermediates to analyze the contribution of each phosphorylation independently. We found that the dynamics of Aurora and IN-box are interconnected, and IN-box plays both positive and negative regulatory roles depending on the phosphorylation status of the enzyme complex. Phosphorylation in the activation loop of Aurora B occurs intramolecularly and prepares the enzyme complex for activation, but two phosphorylated sites are synergistically responsible for full enzyme activity.

biochemistry↗

bioRxiv2019

CryoEM structure of human CENP-A nucleosome alone and in complex with central domain of human CENP-C

Centromeres are defined epigenetically by nucleosomes containing the histone H3 variant CENP-A, upon which the constitutive centromere-associated network of proteins (CCAN) is built. CENP-C, is considered to be a central organizer of the CCAN. We provide new molecular insights into the structure of CENP-A nucleosomes, in isolation and in complex with the CENP-C central region (CENP-CCR), the main CENP-A binding module of CENP-C. We establish that the short N-helix of CENP-A promotes DNA flexibility at the nucleosome ends, independently of the sequence it wraps.\n\nFurthermore, we show that, in vitro, two regions of CENP-C (CENP-CCR and CENP-Cmotif) both bind exclusively to the CENP-A nucleosome. We find CENP-CCR to bind with high affinity due to an extended hydrophobic area made up of CENP-AV532 and CENP-AV533. Importantly, we identify two key conformational changes within the CENP-A nucleosome upon CENP-C binding. First, the loose DNA wrapping of CENP-A nucleosomes is further exacerbated, through destabilization of the H2A N-terminal tail. Second, CENP-CCR rigidifies the N-terminal tail of H4 in the conformation favoring H4K20 monomethylation, essential for a functional centromere.\n\nSynopsisCENP-A nucleosomes have a short N helix incompatible with complete DNA wrapping, independently of DNA sequence. CENP-C binds exclusively to CENP-A nucleosomes and this binding induces conformational changes that further differentiate CENP-A-containing from canonical nucleosomes.\n\nO_LICENP-C binds CENP-A nucleosomes specifically\nC_LIO_LIDNA ends of the CENP-A nucleosome are further unwrapped in the CENP-A/CENP-C complex, due to flexible H2A C-terminal tails\nC_LIO_LIThe N-terminal tail of H4 adopts a conformation favored for centromere specific H4K20 monomethylation when CENP-C is bound\nC_LI

biochemistry↗