Nikolina Sekulic

• 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 Full text in Research Archive. Show summary

  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.

• Stonyte, Vilte; Martîn, Ruth Martîn; Segura-Pena, Dario; Sekulic, Nikolina & Lopez Aviles, Sandra (2020). Requirement of PP2A-B56 Par1 for the Stabilization of the CDK Inhibitor Rum1 and Activation of APC/C Ste9 during Pre-Start G1 in S. pombe. iScience.  ISSN 2589-0042.  23(5) . doi: 10.1016/j.isci.2020.101063 Full text in Research Archive. Show summary

  Exit from the cell cycle during the establishment of quiescence and upon cell differentiation requires the sustained inactivation of CDK complexes. Fission yeast cells deprived of nitrogen halt cell cycle progression in pre-Start G1, before becoming quiescent or undergoing sexual differentiation. The CDK inhibitor Rum1 and the APC/C activator Ste9 are fundamental for this arrest, but both are down-regulated by CDK complexes. Here, we show that PP2A-B56Par1 is instrumental for Rum1 stabilization and Ste9 activation. In the absence of PP2A-B56Par1, cells fail to accumulate Rum1, and this results in persistent CDK activity, Ste9 inactivation, retention of the mitotic cyclin Cdc13, and impaired withdrawal from the cell cycle during nitrogen starvation. Importantly, mutation of a putative B56 interacting motif in Rum1 recapitulates these defects. These results underscore the relevance of CDK-counteracting phosphatases in cell differentiation, establishment of the quiescent state, and escape from it in cancer cells.

• 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 Full text in Research Archive.
• Avgousti, Daphne C.; Herrmann, Christin; Kulej, Katarzyna; Pancholi, Neha J.; Sekulic, Nikolina; Petrescu, Joana; Molden, Rosalynn C.; Blumenthal, Daniel; Paris, Andrew J.; Reyes, Emigdio D.; Ostapchuk, Philomena; Hearing, Patrick; Seeholzer, Steven H.; Worthen, G. Scott; Black, Ben E.; Garcia, Benjamin A. & Weitzman, Matthew D. (2016). A core viral protein binds host nucleosomes to sequester immune danger signals. Nature.  ISSN 0028-0836.  535(7610), s 173- 177 . doi: 10.1038/nature18317
• Falk, Samantha J.; Lee, Jaehyoun; Sekulic, Nikolina; Sennett, Michael A.; Lee, Tae-Hee & Black, Ben E. (2016). CENP-C directs a structural transition of CENP-A nucleosomes mainly through sliding of DNA gyres. Nature Structural & Molecular Biology.  ISSN 1545-9993.  23(3), s 204- 208 . doi: 10.1038/nsmb.3175
• Sekulic, Nikolina & Black, Ben E. (2016). Preparation of Recombinant Centromeric Nucleosomes and Formation of Complexes with Nonhistone Centromere Proteins. Methods in Enzymology.  ISSN 0076-6879.  573, s 67- 96 . doi: 10.1016/bs.mie.2016.01.014 Show summary

  Centromeres are present on each chromosome to direct proper segregation during cell division. The understanding of how the histone H3 variant, CENP-A, epigenetically marks the location of the centromere on the chromosome has been advanced, in part, through the study of histone complexes, nucleosomes, and nucleosomal complexes with nonhistone centromere proteins. In this chapter, we describe the preparation of recombinant versions of these complexes. The methodology is firmly rooted in classic nucleosome reconstitution methods, but we highlight the aspects of the preparations that diverge from those used for the methods established with canonical histones. We also provide a method for producing PCR-amplified nucleosomal DNA sequences in milligram quantities that is particularly useful for studies where multiple sequences and/or chemical modifications are desired. Lastly, we describe our approach to assemble and analyze a complex between the recombinant human CENP-A nucleosome and one of its binding partners, CENP-C.

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• Mojica Cortez, Natalia; Sekulic, Nikolina & Krengel, Ute (2020). UiO Structural Biology Core Facilities: Who Are We and How Can We Help You?.
• Sekulic, Nikolina; Cascella, Michele & Hovet, Oda (2020). Molecular Dynamics Studies on the Essential Mitotic Protein Kinase – Aurora B.

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