Ahmad Ali Ahmad

• Nagpal, Harsh; Ali Ahmad, Ahmad; Hirano, Yasuhiro; Cai, Wei; Halic, Mario & Fukagawa, Tatsuo [Vis alle 8 forfattere av denne artikkelen] (2023). CENP-A and CENP-B collaborate to create an open centromeric chromatin state. Nature Communications. ISSN 2041-1723. 14(1). doi: 10.1038/s41467-023-43739-5. Fulltekst i vitenarkiv Vis sammendrag

  Centromeres are epigenetically defined via the presence of the histone H3 variant CENP-A. Contacting CENP-A nucleosomes, the constitutive centromere associated network (CCAN) and the kinetochore assemble, connecting the centromere to spindle microtubules during cell division. The DNA-binding centromeric protein CENP-B is involved in maintaining centromere stability and, together with CENP-A, shapes the centromeric chromatin state. The nanoscale organization of centromeric chromatin is not well understood. Here, we use single-molecule fluorescence and cryoelectron microscopy (cryoEM) to show that CENP-A incorporation establishes a dynamic and open chromatin state. The increased dynamics of CENP-A chromatin create an opening for CENP-B DNA access. In turn, bound CENP-B further opens the chromatin fiber structure and induces nucleosomal DNA unwrapping. Finally, removal of CENP-A increases CENP-B mobility in cells. Together, our studies show that the two centromere-specific proteins collaborate to reshape chromatin structure, enabling the binding of centromeric factors and establishing a centromeric chromatin state.

• Ali Ahmad, Ahmad & Sekulic, Nikolina (2020). CENP-A nucleosome-a chromatin-embedded pedestal for the centromere: lessons learned from structural biology. Essays in Biochemistry. ISSN 0071-1365. 64(2), s. 205–221. doi: 10.1042/EBC20190074. Fulltekst i vitenarkiv Vis sammendrag

  The centromere is a chromosome locus that directs equal segregation of chromosomes during cell division. A nucleosome containing the histone H3 variant CENP-A epigenetically defines the centromere. Here, we summarize findings from recent structural biology studies, including several CryoEM structures, that contributed to elucidate specific features of the CENP-A nucleosome and molecular determinants of its interactions with CENP-C and CENP-N, the only two centromere proteins that directly bind to it. Based on those findings, we propose a role of the CENP-A nucleosome in the organization of centromeric chromatin beyond binding centromeric proteins.

• Ali Ahmad, Ahmad; Bilokapic, Silvija; Schafer, Ingmar B; Halic, Mario & Sekulic, Nikolina (2019). CENP‐C unwraps the human CENP‐A nucleosome through the H2A C‐terminal tail. EMBO Reports. ISSN 1469-221X. doi: 10.15252/embr.201948913. Fulltekst i vitenarkiv

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