Structural insights into the N-terminal APHB domain of HrpA: mediating canonical and i-motif recognition

RNA helicases function as versatile enzymes primarily responsible for remodeling RNA secondary structures and organizing ribonucleoprotein complexes. In our study, we conducted a systematic analysis of the helicase-related activities of Escherichia coli HrpA and presented the structures of both its apo form and its complex bound with both conventional and non-canonical DNAs. Our findings reveal that HrpA exhibits NTP hydrolysis activity and binds to ssDNA and ssRNA in distinct sequence-dependent manners. While the helicase core plays an essential role in unwinding RNA/RNA and RNA/DNA duplexes, the N-terminal extension in HrpA, consisting of three helices referred to as the APHB domain, is crucial for ssDNA binding and RNA/DNA duplex unwinding. Importantly, the APHB domain is implicated in binding to non-canonical DNA structures such as G-quadruplex and i-motif, and this report presents the first solved i-motif-helicase complex. This research not only provides comprehensive insights into the multifaceted roles of HrpA as an RNA helicase but also establishes a foundation for further investigations into the recognition and functional implications of i-motif DNA structures in various biological processes.

The catalytic triad of rice NARROW LEAF1 involves H234

NARROW LEAF1 (NAL1) exerts a multifaceted influence on leaf morphology and crop yield. Recent crystal study proposed that histidine 233 (H233) is part of the catalytic triad. Here we report that unlike suggested previously, H234 instead of H233 is a component of the catalytic triad alongside residues D291 and S385 in NAL1. Remarkably, residue 233 unexpectedly plays a pivotal role in regulating NAL1's proteolytic activity. These findings establish a strong foundation for utilizing NAL1 in breeding programs aimed at improving crop yield.

Serum thymidine kinase 1 is a prognostic and monitoring factor in patients with non-small cell lung cancer

Thymidine kinase 1 (TK1) is a pyrimidine metabolic pathway enzyme involved in salvage DNA synthesis and thus, a cell cycle-dependent marker. We have developed anti-TK1 monoclonal/polyclonal Abs raised against a 15-amino acid synthetic peptide (KPGEAVAARKLFAPQ) corresponding to part of the C-terminus of human TK1. These Abs are useful for both serological and immunohistochemical detection of TK1 in a number of cancer diseases. In this study we examined TK1 concentration in serum (STK1) in 250 preoperative non-small cell lung cancer patients (NSCLC), including 188 non-metastatic (group M0) and 62 metastatic patients (group M1). Serum from 16 healthy individuals was used as controls. The concentration of STK1 of preoperative NSCLC patients was significantly higher than STK1 of healthy individuals (p<0.0001). In group M0, preoperative STK1 concentration was significantly higher in patients of tumour size T2, as compared to tumour size T1 (p=0.042), and in T3-T4, as compared to T1-T2 (p=0.01). No significant difference in STK1 concentration between patients of tumour stage I and stage II (p=0.057) were found, but significantly higher STK1 concentration in patients of stage III, as compared stage I-II (p=0.025). No significant difference of STK1 concentration were found in patients of group M1 concerning tumour size or tumour stage, or between patients with adenocarcinomas (AC) and squamous cell carcinomas (SCC). We studied the changes of STK1 concentration individually one month after operation in metastatic subjects (group M1, n=19) and in tumour-free subjects (group M0, n=38). In the M0 group, the concentration of STK1 one month after operation was significantly decline by 45%, when comparing to concentrations of STK1 preoperative (p<0.001). In the group M1, however, no significant decrease in STK1 concentrations were found one month after operation. We conclude that STK1 has prognostic value and is a reliable marker for monitoring the response to surgery of NSCLC patients.