Modulation effect of double strand DNA on the self-assembly of N-terminal domain of Euplotes octocarinatus centrin

Methods for Assessment of Nucleotide Excision Repair Efficiency

Nucleotide excision repair (NER) is responsible for removing a wide variety of bulky adducts from DNA, thus contributing to the maintenance of genome stability. The efficiency with which proteins of the NER system recognize and remove bulky adducts depends on many factors and is of great clinical and diagnostic significance. The review examines current concepts of the NER system molecular basis in eukaryotic cells and analyzes methods for the assessment of the NER-mediated DNA repair efficiency both in vitro and ex vivo.

Phosphorylation promotes the endonuclease-like activity of human centrin 2

Centrin is a member of the EF-hand superfamily of calcium-binding proteins, which is involved in the nucleotide excision repair (NER). Reversible phosphorylation of centrin is an important regulatory mechanism in vivo and is closely related to many physiological processes. To explore the possible role of centrin in NER, the endonuclease-like activity of human centrin 2 (HsCen2) regulated by phosphorylation in the absence or presence of Tb³⁺ was investigated by spectroscopy techniques, gel electrophoresis, and molecular docking simulation in 10 mM Hepes, pH 7.4. The results showed that phosphorylation weakened the binding of Tb³⁺ to HsCen2 and enhanced the binding of DNA to HsCen2. Phosphorylation improves the endonuclease-like activity of HsCen2. In addition, Tb³⁺ is favorable for DNA binding and endonuclease-like activity of HsCen2 before and after phosphorylation. These results provide clear insights into the effects of phosphorylation on the properties of HsCen2 and offer important clues for further exploration of how phosphorylation affects protein-driven functions.

Phosphorylation weakened the binding of Tb³⁺ to HsCen2, enhanced the binding of DNA to HsCen2; and improves the endonuclease-like activity of HsCen2; Additionally, the endonuclease-like activity of HsCen2 or HsCen2p is regulated up by Tb³⁺-binding.

N‑(6‑Aminohexyl)‑5‑chloro‑1‑naphthalenesulfonamide, a centrin antagonist, inhibits Tb3+/peptides-binding properties

N‑(6‑Aminohexyl)‑5‑chloro‑1‑naphthalenesulfonamide (W-7), a kind of adjuvant chemotherapy, can bind to calmodulin and inhibit Ca²⁺/calmodulin-regulated enzyme activities and cell proliferation. Similar to calmodulin, euplotes octocarinatus centrin (EoCen) belongs to EF-hand superfamily of calcium-binding proteins. It is associated with nucleotide excision repair (NER), cell division cycle and ciliogenesis. In the present study, the comparative interaction of W-7 with EoCen was first examined by using various spectroscopic, calorimetric methods and molecular docking. The obtain results recommend that only one W-7 molecule is identified binding to the C-terminal hydrophobic pocket of centrin that normally plays a role in anchoring targets. Methyl groups of Ala126, Met141, Ile161 and M162 of C-terminal may react with W-7 chloronaphthalene ring, other aliphatic or aromatic side-chains in a deep hydrophobic pocket of protein. Circular dichroism (CD) and fluorescence lifetime experiments reveal that W-7 triggers a conformational change of centrin. As a result, W-7 is identified to be an antagonist of centrin. It appears to inhibit the centrin-mediated activation of target proteins by blocking the hydrophobic pocket. Moreover, the complex formation leads to affinity decrease of Tb³⁺ binding to C-terminal of protein and self-assembly affected. Our present study provides the first view of centrin recognizing a naphthalene-sulfonamide derivative. It is proposed that W-7 and its analogues can serve as a useful tool for research on the participation of centrin in biological processes and cell biology-related studies.

Inhibitory effect of melittin on endonuclease-like activity of centrin

The xeroderma pigmentosum group C protein (XPC) and centrin2 are the primary initiators of global genome nucleotide excision repair (NER). Centrin, acts as a member of the EF-hand super family of calcium-binding proteins, playing roles in reconstitution of the vitro NER reaction. To understand the possible molecular and structural properties of the multiprotein process, the interactions of Euplotes octocarinatus centrin (EoCen), melittin, and DNA are described. EoCen shares a sequence identity of 66% with centrin2. Melittin possesses inverse direction hydrophobic triads-leucine-leucine-tryptophan (LLW) which are responsible for centrin binding. It is applied as a natural peptide to mimic centrin target peptide. As a result, it is proved that the integrated protein shows an endonuclease-like activity to DNA. Melittin is capable of interaction with both EoCen and DNA. More importantly, it is found that melittin displays an inhibitory effect on the endonuclease-like activity of centrin when it co-exists with EoCen and DNA in solution. Meanwhile, the DNA-melittin-EoCen ternary complex forms in the process. Quantitative analyses demonstrated by extensive biophysical assays reveal that binding of the peptide to DNA or centrin modulates the binding properties of it to another component. Furthermore, a possible positioning model of DNA and EoCen on melittin is proposed. This finding may constitute a model for that existing between centrin and its target peptide in NER process.