Browsing by Author "Kuppa, Sahiti"

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An Aurora B-RPA signaling axis secures chromosome segregation fidelity
(Springer Science and Business Media LLC, 2023-05) Roshan, Poonam; Kuppa, Sahiti; Mattice, Jenna R.; Kaushik, Vikas; Chadda, Rahul; Pokhrel, Nilisha; Tumala, Brunda R.; Biswas, Aparna; Bothner, Brian; Antony, Edwin; Origanti, Sofia
Errors in chromosome segregation underlie genomic instability associated with cancers. Resolution of replication and recombination intermediates and protection of vulnerable single-stranded DNA (ssDNA) intermediates during mitotic progression requires the ssDNA binding protein Replication Protein A (RPA). However, the mechanisms that regulate RPA specifically during unperturbed mitotic progression are poorly resolved. RPA is a heterotrimer composed of RPA70, RPA32 and RPA14 subunits and is predominantly regulated through hyperphosphorylation of RPA32 in response to DNA damage. Here, we have uncovered a mitosis-specific regulation of RPA by Aurora B kinase. Aurora B phosphorylates Ser-384 in the DNA binding domain B of the large RPA70 subunit and highlights a mode of regulation distinct from RPA32. Disruption of Ser-384 phosphorylation in RPA70 leads to defects in chromosome segregation with loss of viability and a feedback modulation of Aurora B activity. Phosphorylation at Ser-384 remodels the protein interaction domains of RPA. Furthermore, phosphorylation impairs RPA binding to DSS1 that likely suppresses homologous recombination during mitosis by preventing recruitment of DSS1-BRCA2 to exposed ssDNA. We showcase a critical Aurora B-RPA signaling axis in mitosis that is essential for maintaining genomic integrity.
Dynamic states of eIF6 and SDS variants modulate interactions with uL14 of the 60S ribosomal subunit
(Oxford University Press, 2023-01) Elliff, Jonah; Biswas, Aparna; Roshan, Poonam; Kuppa, Sahiti; Patterson, Angela; Mattice, Jenna; Chinnaraj, Mathivanan; Burd, Ryan; Walker, Sarah E; Pozzi, Nicola; Antony, Edwin; Bothner, Brian; Origanti, Sofia
Assembly of ribosomal subunits into active ribosomal complexes is integral to protein synthesis. Release of eIF6 from the 60S ribosomal subunit primes 60S to associate with the 40S subunit and engage in translation. The dynamics of eIF6 interaction with the uL14 (RPL23) interface of 60S and its perturbation by somatic mutations acquired in Shwachman–Diamond Syndrome (SDS) is yet to be clearly understood. Here, by using a modified strategy to obtain high yields of recombinant human eIF6 we have uncovered the critical interface entailing eight key residues in the C-tail of uL14 that is essential for physical interactions between 60S and eIF6. Disruption of the complementary binding interface by conformational changes in eIF6 disease variants provide a mechanism for weakened interactions of variants with the 60S. Hydrogen–deuterium exchange mass spectrometry (HDX-MS) analyses uncovered dynamic configurational rearrangements in eIF6 induced by binding to uL14 and exposed an allosteric interface regulated by the C-tail of eIF6. Disrupting key residues in the eIF6–60S binding interface markedly limits proliferation of cancer cells, which highlights the significance of therapeutically targeting this interface. Establishing these key interfaces thus provide a therapeutic framework for targeting eIF6 in cancers and SDS.
Rtt105 regulates RPA function by configurationally stapling the flexible domains
(Springer Science and Business Media LLC, 2022-09) Kuppa, Sahiti; Deveryshetty, Jaigeeth; Chadda, Rahul; Mattice, Jenna R.; Pokhrel, Nilisha; Kaushik, Vikas; Patterson, Angela; Dhingra, Nalini; Pangeni, Sushil; Sadauskas, Marisa K.; Shiekh, Sajad; Balci, Hamza; Ha, Taekjip; Zhao, Xiaolan; Bothner, Brian; Antony, Edwin
Replication Protein A (RPA) is a heterotrimeric complex that binds to single-stranded DNA (ssDNA) and recruits over three dozen RPA-interacting proteins to coordinate multiple aspects of DNA metabolism including DNA replication, repair, and recombination. Rtt105 is a molecular chaperone that regulates nuclear localization of RPA. Here, we show that Rtt105 binds to multiple DNA binding and protein-interaction domains of RPA and configurationally staples the complex. In the absence of ssDNA, Rtt105 inhibits RPA binding to Rad52, thus preventing spurious binding to RPA-interacting proteins. When ssDNA is available, Rtt105 promotes formation of high-density RPA nucleoprotein filaments and dissociates during this process. Free Rtt105 further stabilizes the RPA-ssDNA filaments by inhibiting the facilitated exchange activity of RPA. Collectively, our data suggest that Rtt105 sequesters free RPA in the nucleus to prevent untimely binding to RPA-interacting proteins, while stabilizing RPA-ssDNA filaments at DNA lesion sites.