T4 DNA ligase structure reveals a prototypical ATP-dependent ligase with a unique mode of sliding clamp interaction.

DNA ligases play essential roles in DNA replication and repair. Bacteriophage T4 DNA ligase is the first ATP-dependent ligase enzyme to be discovered and is widely used in molecular biology, but its structure remained unknown. Our crystal structure of T4 DNA ligase bound to DNA shows a compact α-helical DNA-binding domain (DBD), nucleotidyl-transferase (NTase) domain, and OB-fold domain, which together fully encircle DNA. The DBD of T4 DNA ligase exhibits remarkable structural homology to the core DNA-binding helices of the larger DBDs from eukaryotic and archaeal DNA ligases, but it lacks additional structural components required for protein interactions. T4 DNA ligase instead has a flexible loop insertion within the NTase domain, which binds tightly to the T4 sliding clamp gp45 in a novel α-helical PIP-box conformation. Thus, T4 DNA ligase represents a prototype of the larger eukaryotic and archaeal DNA ligases, with a uniquely evolved mode of protein interaction that may be important for efficient DNA replication.

Perforated Appendicitis Presenting as a Soft Tissue Infection of the Thigh: An Example of Successful Non-Operative Management.

Perforated appendicitis is a rare but serious clinical scenario typically requiring urgent surgical intervention. Herein, we discuss the case of a 62-year-old woman with COVID-19 and ruptured retrocecal appendicitis presenting as a right lower extremity soft tissue infection that was successfully managed using non-operative measures. This unique case illustrates the feasibility of conservative care - rather than urgent surgical intervention - in the treatment of an atypical presentation of complicated appendicitis in a high-risk patient.

Sex Differences in Patients With Suspected Cardiac Sarcoidosis Assessed by Cardiovascular Magnetic Resonance Imaging.

Background: There are few data on sex differences in suspected cardiac sarcoidosis. Methods: Consecutive patients with histologically proven sarcoidosis and suspected cardiac involvement were studied. We investigated sex differences in presenting features, cardiac involvement, and the long-term incidence of a primary composite end point of all-cause death or significant ventricular arrhythmia and secondary end points of all-cause death and significant ventricular arrhythmia. Results: Among 324 patients, 163 (50.3%) were female and 161 (49.7%) were male patients. Female patients had a greater prevalence of chest pain (37.4% versus 23.6%; P=0.010) and palpitations (39.3% versus 26.1%; P=0.016) than male patients but not dyspnea, presyncope, syncope, or arrhythmias at presentation. Female patients had a lower prevalence of late gadolinium enhancement on cardiovascular magnetic resonance imaging (20.2% versus 35.4%; P=0.003) and less often met criteria for a clinical diagnosis of cardiac sarcoidosis (Heart Rhythm Society consensus criteria, 22.7% versus 36.0%; P=0.012 and 2016 Japanese Circulation Society guideline criteria, 8.0% versus 19.3%; P=0.005), indicating lesser cardiac involvement. However, the long-term incidence of all-cause death or significant ventricular arrhythmia was not different between female and male patients (23.2% versus 23.2%; P=0.46). Among the secondary end points, the incidence of all-cause death was not different between female and male patients (20.7% versus 14.3%; P=0.51), while female patients had a lower incidence of significant ventricular arrhythmia compared with male patients (4.3% versus 13.0%; P=0.022). On multivariable analyses, sex was not associated with the primary end point (hazard ratio for female patients, 1.36 [95% CI, 0.77­2.43]; P=0.29). Conclusions: We observed distinct sex differences in patients with suspected cardiac sarcoidosis. A paradox was identified wherein female patients had a greater prevalence of chest pain and palpitations than male patients, but lesser cardiac involvement, and a similar long-term incidence of all-cause death or significant ventricular arrhythmia.

An Undergraduate Surgery Interest Group: Introducing Premedical Students to the Practice of Surgery.

PURPOSE: Early exposure and surgical mentorship can augment interest in surgery. We evaluate the effect and feasibility of offering education and mentorship opportunities in surgery to premedical students at our institution through an undergraduate surgery interest group (USIG). MATERIALS AND METHODS: We conducted a 1-year assessment of our USIG and reviewed its organizational structure, funding resources, media promotion, and educational activities. Our USIG hosted introductory-level surgical skills workshops, guest lectures by surgeons, and various facility tours. To assess participants' interests, as well as the influences on them to pursue a surgical profession, we analyzed pre- and post-event questionnaires. Similar questionnaires were completed by medical students in our medical student surgery interest group to compare any differences in perception between premedical and medical students. RESULTS: Our USIG currently has 378 undergraduate student members, with a higher proportion of women than in our medical student surgery interest group (P < 0.003). Neurosurgery was the most popular career choice among undergraduate participants. Participants reported the highest satisfaction with suturing and high-fidelity trauma surgery skills workshops. Undergraduate participants indicated that their intrinsic interest in the sciences is the highest motivation to pursue a surgical profession. Resident lifestyle and social obligations of a surgical career were actually positive influences for undergraduate participants; in contrast, medical students viewed those variables as negative factors. CONCLUSION: Our USIG was met with enthusiasm by premedical students and faculty alike. Participation strengthened premedical students' interest in pursuing surgery and increased their understanding of the surgical profession. Early mentorship may positively influence premedical students' perception of surgical careers. USIG is economically feasible and time-efficient; we encourage other academic institutions and educators to consider investing in similar interest groups.