Biology subjects

Morstadt, L. M.

Publications and source records attributed to Morstadt, L. M..

3 recordsLinked to original sources

bioRxiv2024

Nsp1 stalls DNA Polymerase alpha at DNA hairpins

The human primosome, a four-subunit complex of DNA primase and DNA polymerase alpha (Pol), plays a critical role in DNA replication by initiating RNA and DNA synthesis on both chromosome strands. A recent study has shown that a major virulence factor in the SARS-CoV-2 infection, Nsp1 (non-structural protein 1), forms a stable complex with Pol but does not affect the primosome activity. Here we show that Nsp1 inhibits DNA synthesis across inverted repeats prone to hairpin formation. Analysis of current structural data revealed the overlapping binding sites for Nsp1 and the winged helix-turn-helix domain of RPA (wHTH) on Pol, indicating a competition between them. Comparison of the inhibitory effect of Nsp1 and wHTH on DNA hairpin bypass by Pol showed an 8-fold lower IC50 value for Nsp1 (1 {micro}M). This study provides a valuable insight into the mechanism of inhibition of human DNA replication by Nsp1 during a SARS-CoV-2 infection.

biochemistry↗

bioRxiv2022

The iron-sulfur cluster is critical for DNA binding by human DNA polymerase ϵ

DNA polymerase {varepsilon} (Pol{varepsilon}) is a key enzyme for DNA replication in eukaryotes. It is attached to a helicase and performs DNA synthesis on the leading strand. Recently it was shown that the catalytic domain of yeast Pol{varepsilon} (Pol{varepsilon}CD) contains a [4Fe-4S] cluster located at the base of the processivity domain (P-domain) and coordinated by four conserved cysteines. In this work, we have shown that human Pol{varepsilon}CD (hPol{varepsilon}CD) expressed in bacterial cells also contains an iron-sulfur cluster. In comparison, recombinant hPol{varepsilon}CD produced in insect cells contains an eight-fold-lower level of iron. Interestingly, the iron content correlates with the level of DNA-binding molecules, which suggests an important role of the iron-sulfur cluster in hPol{varepsilon} interaction with DNA. Indeed, mutation of two conserved cysteines that coordinate the cluster abolished template:primer binding and, therefore, DNA polymerase and proofreading exonuclease activities. We propose that the cluster regulates the conformation of the P-domain, which, like a gatekeeper, controls access to a DNA-binding cleft for a template:primer. In addition, we performed kinetic and binding studies of hPol{varepsilon}CD. The binding studies demonstrated low affinity of hPol{varepsilon}CD to DNA and a strong effect of salt concentration on stability of the hPol{varepsilon}CD/DNA complex. Pre-steady-state kinetic studies have shown a maximal polymerization rate constant of 51.5 s-1 and a relatively low affinity to incoming dNTP with an apparent KD of 105 M. This work provides notable insight into the role of a [4Fe-4S] cluster in Pol{varepsilon} function.

biochemistry↗

bioRxiv2022

Insight into RNA-DNA primer length counting by human primosome

The human primosome, a four-subunit complex of primase and DNA polymerase alpha (Pol), synthesizes chimeric RNA-DNA primers for DNA polymerases delta and epsilon to initiate DNA replication on both chromosome strands. Despite recent structural insights into the action of its two catalytic centers, the mechanism of DNA synthesis termination is still unclear. Here we report results of functional and structural studies revealing how the human primosome counts RNA-DNA primer length and timely terminates DNA elongation. Using a single-turnover primer extension assay, we defined two factors that determine a mature primer length (~35-mer): 1) a tight interaction of the C-terminal domain of the DNA primase large subunit (p58C) with the primer 5-end, and 2) flexible tethering of p58C and the DNA polymerase alpha catalytic core domain (p180core) to the primosome platform domain by extended linkers. The obtained data allows us to conclude that p58C is a key regulator of all steps of RNA-DNA primer synthesis. The above-described findings provide a notable insight into the mechanism of DNA synthesis termination by a eukaryotic primosome, an important process for ensuring successful primer handover to replication DNA polymerases and for maintaining genome integrity.

biochemistry↗