Influence of the T to S mutation at the STMK motif on antibiotic resistance of penicillin binding protein 1A: A comprehensive computational study

Peptidoglycan biosynthesis-associated enzymatic kinetic characteristics and β-lactam antibiotic inhibitory effects of different Streptococcus pneumoniae penicillin-binding proteins

Penicillin-binding proteins (PBPs) include transpeptidases, carboxypeptidases, and endopeptidases for biosynthesis of peptidoglycans in the cell wall to maintain bacterial morphology and survival in the environment. Streptococcus pneumoniae expresses six PBPs, but their enzymatic kinetic characteristics and inhibitory effects on different β-lactam antibiotics remain poorly understood. In this study, all the six recombinant PBPs of S. pneumoniae displayed transpeptidase activity with different substrate affinities (Km = 1.56-9.11 mM) in a concentration-dependent manner, and rPBP3 showed a greater catalytic efficiency (Kcat = 2.38 s-1) than the other rPBPs (Kcat = 3.20-7.49 × 10-2 s-1). However, only rPBP3 was identified as a carboxypeptidase (Km = 8.57 mM and Kcat = 2.57 s-1). None of the rPBPs exhibited endopeptidase activity. Penicillin and cefotaxime inhibited the transpeptidase and carboxypeptidase activity of all the rPBPs but imipenem did not inhibited the enzymatic activities of rPBP3. Except for the lack of binding of imipenem to rPBP3, penicillin, cefotaxime, and imipenem bound to all the other rPBPs (KD = 3.71-9.35 × 10-4 M). Sublethal concentrations of penicillin, cefotaxime, and imipenem induced a decrease of pneumococcal pbps-mRNA levels (p < 0.05). These results indicated that all six PBPs of S. pneumoniae are transpeptidases, while only PBP3 is a carboxypeptidase. Imipenem has no inhibitory effect on pneumococcal PBP3. The pneumococcal genes for encoding endopeptidases remain to be determined.

β-lactam Resistance in Pseudomonas aeruginosa: Current Status, Future Prospects

Pseudomonas aeruginosa is a major opportunistic pathogen, causing a wide range of acute and chronic infections. β-lactam antibiotics including penicillins, carbapenems, monobactams, and cephalosporins play a key role in the treatment of P. aeruginosa infections. However, a significant number of isolates of these bacteria are resistant to β-lactams, complicating treatment of infections and leading to worse outcomes for patients. In this review, we summarize studies demonstrating the health and economic impacts associated with β-lactam-resistant P. aeruginosa. We then describe how β-lactams bind to and inhibit P. aeruginosa penicillin-binding proteins that are required for synthesis and remodelling of peptidoglycan. Resistance to β-lactams is multifactorial and can involve changes to a key target protein, penicillin-binding protein 3, that is essential for cell division; reduced uptake or increased efflux of β-lactams; degradation of β-lactam antibiotics by increased expression or altered substrate specificity of an AmpC β-lactamase, or by the acquisition of β-lactamases through horizontal gene transfer; and changes to biofilm formation and metabolism. The current understanding of these mechanisms is discussed. Lastly, important knowledge gaps are identified, and possible strategies for enhancing the effectiveness of β-lactam antibiotics in treating P. aeruginosa infections are considered.

Insights into resistance mechanism of hepatitis C virus nonstructural 3/4A protease mutant to boceprevir using umbrella sampling simulation study

Hepatitis C virus can cause inflammation in human liver cells, leading to liver cirrhosis and liver cancer. Based on the World Health Organization reports, about 228 million people in the world have hepatitis C. To date, some inhibitory medicines against the hepatitis C virus nonstructural 3/4A protease, such as boceprevir, have entered clinical trial phases. However, several hepatitis C virus nonstructural 3/4A protease mutations have been recognized to decrease susceptibility of boceprevir to hepatitis C virus. The molecular details behind inhibitor resistance of these single-point mutations are not still understood. Thus, in this research, computational strategies were applied to clarify the inhibitor resistance mechanism. From umbrella sampling simulation and energy profiles, the polar interactions are the main driving force for boceprevir binding. Based on the analyzed R155T mutant, the main reason for the occurrence of boceprevir resistance is the conformation alterations of S4 and extended S2 binding pockets. These changes, lead to decreased binding ability of the key residues to P2 and P4 moieties of boceprevir. Moreover, structural results show that the disappearance of important salt bridges can bring about the great conformation changes of the binding pockets in R155T.Communicated by Ramaswamy H. Sarma.