Lewandowski, E. M. | bioRxiv Science

bioRxiv2022

Naturally occurring mutations of SARS-CoV-2 main protease confer drug resistance to nirmatrelvir

The SARS-CoV-2 main protease (Mpro) is the drug target of Pfizers oral drug Paxlovid. The emergence of SARS-CoV-2 variants with mutations in Mpro raised the alarm of potential drug resistance. In this study, we identified 100 naturally occurring Mpro mutations located at the nirmatrelvir binding site, among which 20 mutants, including S144M/F/A/G/Y, M165T, E166G, H172Q/F, and Q192T/S/L/A/I/P/H/V/W/C/F, showed comparable enzymatic activity to the wild-type (kcat/Km <10-fold change) and resistance to nirmatrelvir (Ki >10-fold increase). X-ray crystal structures were determined for seven representative mutants with and/or without GC-376/nirmatrelvir. Viral growth assay showed that Mpro mutants with reduced enzymatic activity led to attenuated viral replication. Overall, our study identified several drug resistant hot spots that warrant close monitoring for possible clinical evidence of Paxlovid resistance. One Sentence SummaryPaxlovid resistant SARS-CoV-2 viruses with mutations in the main protease have been identified from clinical isolates.

pharmacology and toxicology↗

bioRxiv2022

A unique class of Zn2+-binding PBPs underlies cephalosporin resistance and sporogenesis in Clostridioides difficile

{beta}-Lactam antibiotics, particularly cephalosporins, are major risk factors for C. difficile infection (CDI), the most common hospital acquired infection. These broad-spectrum antibiotics irreversibly inhibit penicillin-binding proteins (PBPs), essential enzymes that assemble the bacterial cell wall. Little is known about the C. difficile PBPs, yet they play central roles in the growth, infection, and transmission of this pathogen. In this study we discover that PBP2, essential for vegetative growth, is the primary bactericidal target for {beta}-lactams in C. difficile. We further demonstrate PBP2 is insensitive to cephalosporin inhibition, revealing a key cause of the well-documented, but poorly understood, cephalosporin resistance in C. difficile. For the first time, we determine the crystal structures of C. difficile PBP2, which bears several highly unique features, including significant ligand-induced conformational changes and an active site Zn2+-binding motif that influences {beta}-lactam binding and protein stability. Remarkably, this motif is shared in two other C. difficile PBPs essential for sporulation, PBP3 and SpoVD. While these PBPs are present in a wide range of bacterial taxa, including species in extreme environments and the human gut, they are mostly found in anaerobes, typically Firmicutes. The widespread presence of this convergently evolved thiol-containing motif and its cognate Zn2+ suggests it may function as a redox-sensor to regulate cell wall synthesis for survival in adverse environments. Collectively, our findings address important etiological questions surrounding C. difficile, characterize new elements of PBP structure and function, and lay the groundwork for antibiotic development targeting both C. difficile growth and sporulation.

microbiology↗