Micrococcin cysteine-to-thiazole conversion through transient interactions between the scaffolding protein TclI and the modification enzymes TclJ and TclN.

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a broad group of compounds mediating microbial competition in nature. Azole/azoline heterocycle formation in the peptide backbone is a key step in the biosynthesis of many RiPPs. Heterocycle formation in RiPP precursors is often carried out by a scaffold protein, an ATP-dependent cyclodehydratase, and an FMN-dependent dehydrogenase. It has generally been assumed that the orchestration of these modifications is carried out by a stable complex including the scaffold, cyclodehydratase, and dehydrogenase. The antimicrobial RiPP micrococcin begins as a precursor peptide (TclE) with a 35-amino acid N-terminal leader and a 14-amino acid C-terminal core containing six Cys residues that are converted to thiazoles. The putative scaffold protein (TclI) presumably presents the TclE substrate to a cyclodehydratase (TclJ) and a dehydrogenase (TclN) to accomplish the two-step installation of the six thiazoles. In this study, we identify a minimal TclE leader region required for thiazole formation, demonstrate complex formation between TclI, TclJ, and TclN, and further define regions of these proteins required for complex formation. Our results point to a mechanism of thiazole installation in which TclI associates with the two enzymes in a mutually exclusive fashion, such that each enzyme competes for access to the peptide substrate in a dynamic equilibrium, thus ensuring complete modification of each Cys residue in the TclE core. IMPORTANCE: Thiopeptides are a family of antimicrobial peptides characterized for having sulfur-containing heterocycles and for being highly post-translationally modified. Numerous thiopeptides have been identified; almost all of which inhibit protein synthesis in gram-positive bacteria. These intrinsic antimicrobial properties make thiopeptides promising candidates for the development of new antibiotics. The thiopeptide micrococcin is synthesized by the ribosome and undergoes several post-translational modifications to acquire its bioactivity. In this study, we identify key interactions within the enzymatic complex that carries out cysteine to thiazole conversion in the biosynthesis of micrococcin.

Micrococcin cysteine-to-thiazole conversion through transient interactions between a scaffolding protein and two modification enzymes.

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a broad group of compounds mediating microbial competition in nature. Azole/azoline heterocycle formation in the peptide backbone is a key step in the biosynthesis of many RiPPs. Heterocycle formation in RiPP precursors is often carried out by a scaffold protein, an ATP-dependent cyclodehydratase, and an FMN-dependent dehydrogenase. It has generally been assumed that the orchestration of these modifications is carried out by a stable complex including the scaffold, cyclodehydratase and dehydrogenase. The antimicrobial RiPP micrococcin begins as a precursor peptide (TclE) with a 35-amino acid N-terminal leader and a 14-amino acid C-terminal core containing six Cys residues that are converted to thiazoles. The putative scaffold protein (TclI) presumably presents the TclE substrate to a cyclodehydratase (TclJ) and a dehydrogenase (TclN) to accomplish the two-step installation of the six thiazoles. In this study, we identify a minimal TclE leader region required for thiazole formation, we demonstrate complex formation between TclI, TclJ and TclN, and further define regions of these proteins required for complex formation. Our results point to a mechanism of thiazole installation in which TclI associates with the two enzymes in a mutually exclusive fashion, such that each enzyme competes for access to the peptide substrate in a dynamic equilibrium, thus ensuring complete modification of each Cys residue in the TclE core.

Visualizing the malperfusion effect of coronary occlusion as a sequela of limited type A aortic dissection.

Limited type A aortic dissection (LTAAD) is a rare subtype of dissection that is confined within a well-defined border of the ascending aorta. These dissections may occur in the remaining native portion of the aortic root following aortic root replacement and can be complicated by malperfusion syndrome-a syndrome where dissections compromise the aortic branches and lead to end-organ ischemia. Because LTAAD is confined within the ascending aorta, malperfusion syndrome may preferentially affect the coronary arteries resulting in coronary malperfusion, myocardial infarction, and increased mortality. We report a case of LTAAD and malperfusion syndrome of the left main coronary artery which resulted in inadequate contrast opacification of the aorta and failure of the dissection protocol to trigger on computed tomography (CT). Upon further evaluation of the situation, the radiologist oversaw the manual triggering of CT acquisitions which yielded an actionable CT at 6 minutes post-contrast and real-time visualization of the patient's developing cardiac ischemia.

Perineal hernia as a sequela of anal reconstruction surgeries in perianal Crohn's disease.

Perineal hernia is a rare complication of pelvic surgeries that can occur in patients with perianal Crohn's disease (pCD) as a long-term outcome of surgeries for complex fistula treatment. We present a case of a symptomatic pCD male patient with multiple perianal surgeries who presents with anal pain, diarrhea, and discharge. Magnetic resonance imaging showed a perineal hernia in the ischioanal fossa violating the convergence of the left external sphincter complex. The hernia was treated with an open primary hernia repair via the perineal approach. It recurred after 3 months, and the patient underwent secondary hernia repair with gracilis muscle interposition and mesh placement. Unfortunately, this was complicated by superficial skin dehiscence and mesh extrusion, but the flap remained viable and the hernia repair was intact. Incidence, symptoms, risk factors, imaging findings, and management of perineal hernias are reviewed.