Resistance to β-lactams is one of the most serious problems associated with Gram-negative infections. β-Lactamases are able to hydrolyze β-lactams such as cephalosporins and/or carbapenems. Evolutionary origin of metallo-β-lactamases (MBLs), conferring critical antibiotic resistance threats, remains unknown. We discovered PNGM-1, the novel subclass B3 MBL, in deep-sea sediments that predate the antibiotic era. Here, our phylogenetic analysis suggests that PNGM-1 yields insights into the evolutionary origin of subclass B3 MBLs. We reveal the structural similarities between tRNase Zs and PNGM-1, and demonstrate that PNGM-1 has both MBL and tRNase Z activities, suggesting that PNGM-1 is thought to have evolved from a tRNase Z. We also show kinetic and structural comparisons between PNGM-1 and other proteins including subclass B3 MBLs and tRNase Zs. These comparisons revealed that the B3 MBL activity of PNGM-1 is a promiscuous activity and subclass B3 MBLs are thought to have evolved through PNGM-1 activity.

Background. Although the incidence of pregnancy-associated pyogenic sacroiliitis is low, it is associated with significant morbidity and mortality. Timely diagnosis of the condition is challenging due to its nonspecific clinical features. Case. A 31-year-old primigravida had an uncomplicated pregnancy and labour. Postpartum, she developed persistent fever and debilitating hip pain on ambulation. White cell count was normal (7.3 × 109/L) and C-reactive protein was elevated (468.4 mg/L). Streptococcus pyogenes was identified on vaginal swabs and blood cultures, and a pelvic magnetic resonance imaging scan revealed bilateral sacroiliitis. Conclusion. Pyogenic sacroiliitis is a potentially lethal cause of postpartum pain. It should be considered as a differential diagnosis even in low-risk women who present with debilitating pelvic pain in or around pregnancy, particularly when initial therapy appears unsuccessful.

The increasing incidence of community- and hospital-acquired infections with multidrug-resistant (MDR) bacteria poses a critical threat to public health and the healthcare system. Although β-lactam antibiotics are effective against most bacterial infections, some bacteria are resistant to β-lactam antibiotics by producing β-lactamases. Among β-lactamases, metallo-β-lactamases (MBLs) are especially worrisome as only a few inhibitors have been developed against them. In MBLs, the metal ions play an important role as they coordinate a catalytic water molecule that hydrolyzes β-lactam rings. We determined the crystal structures of different variants of PNGM-1, an ancient MBL with additional tRNase Z activity. The variants were generated by site-directed mutagenesis targeting metal-coordinating residues. In PNGM-1, both zinc ions are coordinated by six coordination partners in an octahedral geometry, and the zinc-centered octahedrons share a common face. Structures of the PNGM-1 variants confirm that the substitution of a metal-coordinating residue causes the loss of metal binding and β-lactamase activity. Compared with PNGM-1, subclass B3 MBLs lack one metal-coordinating residue, leading to a shift in the metal-coordination geometry from an octahedral to tetrahedral geometry. Our results imply that a subtle change in the metal-binding site of MBLs can markedly change their metal-coordination geometry and catalytic activity.

Antibiotic resistance is a steadily increasing global problem which could lead to a fundamental upheaval in clinical care with the potential to return us to the pre-antibiotic era [1][2][3][4] . The production of β-lactamases, a group of enzymes that confer antibiotic resistance in Gram-negative bacteria, is now one of the major barriers in treating Gram-negative infections 5 . β-Lactamases are classified according to their catalytic mechanisms into serine β-lactamases and metallo-β-lactamases 6,7 . There are functional and structural similarities between serine β-lactamases and penicillin-binding proteins, and so serine β-lactamases are thought to have evolved from a penicillin-binding protein 7,8 . Given the functional and structural differences between serine β-lactamases and metallo-β-lactamases, metallo-β-lactamases are thought to have evolved from a protein other than a penicillin-binding protein, but to date this ancestor remains unknown [8][9][10][11] . We discovered PNGM-1, the first subclass B3 metallo-β-lactamase, in deep-sea sediments that predate the antibiotic era 12 . Here we discover the dual activity of PNGM-1, pinpointing the evolutionary origin of subclass B3 metallo-β-lactamases.Phylogenetic analysis suggested that PNGM-1 could yield insights into the evolutionary origin of subclass B3 metallo-β-lactamases. We reveal the structural similarities between tRNase Zs and PNGM-1, which prompted us to investigate their evolutionary relationship and the possibility of them possessing dual enzymatic activities. We demonstrate that PNGM-1 has dual activity with both true metallo-β-lactamase and tRNase Z activity, suggesting that PNGM-1 is thought to have evolved from a tRNase Z.We also show kinetic and structural comparisons between PNGM-1 and other proteins including subclass B3 metallo-β-lactamases and tRNase Zs. These comparisons revealed that the B3 metallo-β-lactamase activity of PNGM-1 is a promiscuous activity and subclass B3 metallo-β-lactamases are thought to have evolved through PNGM-1 activity. Our work provides a foundation for the evolution of tRNase Z into subclass B3 metallo-β-lactamases through the dual activity of PNGM-1.

No abstract