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The impermeable outer membrane ofPseudomonas aeruginosais bypassed by antibacterial proteins known as S-type pyocins. Because of their properties, pyocins are investigated as a potential new class of antimicrobials againstPseudomonasinfections. Their production and modification, however, remains challenging. To address this limitation, we employed automated fast-flow peptide synthesis (AFPS) for the rapid production of a pyocin S2 import domain. The N-terminal domain sequence (PyS2NTD) was synthesized in under 10 hours and purified to yield milligrams quantities of the desired product. To our knowledge, the 217 amino acid sequence of PyS2NTDis among the longest peptides produced from a “single-shot” synthesis, i.e., made in a single stepwise route without the use of ligation techniques. Biophysical characterization of the PyS2NTDwith circular dichroism was consistent with the literature reports. Fluorescently labeled PyS2NTDbinds toP. aeruginosaexpressing the cognate ferripyoverdine receptor (FpvA) and is taken up into the periplasm. This selective uptake was validated with confocal and super resolution microscopy, flow cytometry, and fluorescence recovery after photobleaching (FRAP). These modified, synthetic S-type pyocins domains can be used to probe import mechanisms ofP. aeruginosaand leveraged to develop selective antimicrobial agents that bypass the outer membrane.

Galactofuranose (Galf) is present in glycans critical for the virulence and viability of several pathogenic microbes, including Mycobacterium tuberculosis, yet the monosaccharide is absent from mammalian glycans. Uridine 5'-diphosphate-galactopyranose mutase (UGM) catalyzes the formation of UDP-Galf, which is required to produce Galf-containing glycoconjugates. Inhibitors of UGM have therefore been sought, both as antimicrobial leads and as tools to delineate the roles of Galf in cells. Obtaining cell permeable UGM probes by either design or high throughput screens has been difficult, as has elucidating how UGM binds small molecule, noncarbohydrate inhibitors. To address these issues, we employed structure-based virtual screening to uncover new inhibitor chemotypes, including a triazolothiadiazine series. These compounds are among the most potent antimycobacterial UGM inhibitors described. They also facilitated determination of a UGM-small molecule inhibitor structure, which can guide optimization. A comparison of results from the computational screen and a high-throughput fluorescence polarization (FP) screen indicated that the scaffold hits from the former had been evaluated in the FP screen but missed. By focusing on promising compounds, the virtual screen rescued false negatives, providing a blueprint for generating new UGM probes and therapeutic leads.

The recent ExecutiveOrder by President Trump attempting to ban temporarily the citizens of seven countries (Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen) from entering the United States is having significant consequences within the country and around the world. The Order poses a threat to the health and vitality of science, barring students and scientists from these countries from traveling to the United States to study or to attend conferences. In preventing those members of the international scientific community from traveling beyond U.S. borders without guaranteed safe return, the Executive Order demeans them; in so doing, it demeans us all. Universities and research communities are especially impacted, as major universities have students and often faculty holding passports from one of these seven countries. This temporary ban would affect refugees fleeing war-torn areas, challenging the long-standing notion that the United States is a safe haven for those fleeing persecution and war in addition to being a magnet for talent from every corner of the world. The pages of this journal reflect the geographic, ethnic, and cultural diversity that underpins great science. The ban impacts domestic and global scientific efforts and communities. Science succeeds through the cooperation between collections of individuals and teams around the world discovering and learning from each other. To ensure rapid scientific progress, open communication and exchange between scientists are essential. As scientists, engineers, and clinicians, we have benefited from open interactions and collaborations with visitors and students from all parts of the world as well as through scientific publications and discussions at scientific meetings.

Despite decades of accumulated knowledge about proteins and their post-translational modifications (PTMs), numerous questions remain regarding their molecular composition and biological function. One of the most fundamental queries is the extent to which the combinations of DNA-, RNA- and PTM-level variations explode the complexity of the human proteome. Here, we outline what we know from current databases and measurement strategies including mass spectrometry-based proteomics. In doing so, we examine prevailing notions about the number of modifications displayed on human proteins and how they combine to generate the protein diversity underlying health and disease. We frame central issues regarding determination of protein-level variation and PTMs, including some paradoxes present in the field today. We use this framework to assess existing data and to ask the question, "How many distinct primary structures of proteins (proteoforms) are created from the 20,300 human genes?" We also explore prospects for improving measurements to better regularize protein-level biology and efficiently associate PTMs to function and phenotype.