Characterization of the replication initiator Orc1/Cdc6 from the Archaeon Picrophilus torridus.

Eukaryotic DNA replication is preceded by the assembly of prereplication complexes (pre-RCs) at or very near origins in G1 phase, which licenses origin firing in S phase. The archaeal DNA replication machinery broadly resembles the eukaryal apparatus, though simpler in form. The eukaryotic replication initiator origin recognition complex (ORC), which serially recruits Cdc6 and other pre-RC proteins, comprises six components, Orc1-6. In archaea, a single gene encodes a protein similar to both the eukaryotic Cdc6 and the Orc1 subunit of the eukaryotic ORC, with most archaea possessing one to three Orc1/Cdc6 orthologs. Genome sequence analysis of the extreme acidophile Picrophilus torridus revealed a single Orc1/Cdc6 (PtOrc1/Cdc6). Biochemical analyses show MBP-tagged PtOrc1/Cdc6 to preferentially bind ORB (origin recognition box) sequences. The protein hydrolyzes ATP in a DNA-independent manner, though DNA inhibits MBP-PtOrc1/Cdc6-mediated ATP hydrolysis. PtOrc1/Cdc6 exists in stable complex with PCNA in Picrophilus extracts, and MBP-PtOrc1/Cdc6 interacts directly with PCNA through a PIP box near its C terminus. Furthermore, PCNA stimulates MBP-PtOrc1/Cdc6-mediated ATP hydrolysis in a DNA-dependent manner. This is the first study reporting a direct interaction between Orc1/Cdc6 and PCNA in archaea. The bacterial initiator DnaA is converted from an active to an inactive form by ATP hydrolysis, a process greatly facilitated by the bacterial ortholog of PCNA, the ß subunit of Pol III. The stimulation of PtOrc1/Cdc6-mediated ATP hydrolysis by PCNA and the conservation of PCNA-interacting protein motifs in several archaeal PCNAs suggest the possibility of a similar mechanism of regulation existing in archaea. This mechanism may involve other yet to be identified archaeal proteins.

Longitudinal analysis and treatment of neuropsychiatric symptoms in post-acute sequelae of COVID-19.

BACKGROUND: Persistent neuropsychiatric symptoms following acute COVID-19 infection are frequently reported. These include anxiety, depression, difficulty concentrating, fatigue, and insomnia. The longitudinal evolution of this neuropsychiatric burden is poorly understood and clinical guidelines concerning treatment are lacking. OBJECTIVE: We sought to describe the longitudinal evolution of neuropsychiatric symptoms in the post-acute sequelae of COVID-19 (PASC) syndrome and examine symptom treatment at a single center. METHODS: Consecutive participants experiencing persistent neurologic symptoms after acute COVID-19 infection were recruited from October 2020 to July 2022. Data collected included COVID-19 infection history, neurological exam and review of systems, Montreal Cognitive Assessment (MoCA), and self-reported surveys concerning neuropsychiatric symptoms and treatment. Data were collected at baseline and at 1-year follow-up. RESULTS: A total of 106 participants (mean age 48.6, females 67%) were included in the study. At 1-year follow-up, 72.5% of participants reported at least one neuropsychiatric symptom. Over half (52.5%) of participants reported persistent fatigue. At baseline, 38.8% of all participants had met the established MoCA cut-off score of < 26 for mild cognitive impairment; this decreased to 20.0% at 1 year. COVID-19 infection severity was associated with neuro-PASC symptoms (including fatigue and anxiety) at 1 year. Overall, 29% of participants started at least one new medication for COVID-19-associated neuropsychiatric symptoms. Of the participants who started new medications, fatigue was the most common indication (44.8%) followed by insomnia (27.6%). CONCLUSIONS: Neuropsychiatric symptoms related to neuro-PASC improve over time but can persist for over a year post-recovery. Most treatment modalities targeted neuro-PASC fatigue.

Characterization of the MCM homohexamer from the thermoacidophilic euryarchaeon Picrophilus torridus.

The typical archaeal MCM exhibits helicase activity independently in vitro. This study characterizes MCM from the euryarchaeon Picrophilus torridus. While PtMCM hydrolyzes ATP in DNA-independent manner, it displays very poor ability to unwind DNA independently, and then too only under acidic conditions. The protein exists stably in complex with PtGINS in whole cell lysates, interacting directly with PtGINS under neutral and acidic conditions. GINS strongly activates MCM helicase activity, but only at low pH. In consonance with this, PtGINS activates PtMCM-mediated ATP hydrolysis only at low pH, with the amount of ATP hydrolyzed during the helicase reaction increasing more than fifty-fold in the presence of GINS. While the stimulation of MCM-mediated helicase activity by GINS has been reported in MCMs from P.furiosus, T.kodakarensis, and very recently, T.acidophilum, to the best of our knowledge, this is the first report of an MCM helicase demonstrating DNA unwinding activity only at such acidic pH, across all archaea and eukaryotes. PtGINS may induce/stabilize a conducive conformation of PtMCM under acidic conditions, favouring PtMCM-mediated DNA unwinding coupled to ATP hydrolysis. Our findings underscore the existence of divergent modes of replication regulation among archaea and the importance of investigating replication events in more archaeal organisms.