Molecular analyses identifies new domains and structural differences among Streptococcus pneumoniae immune evasion proteins PspC and Hic

The choline-binding proteins PspA, PspC, and LytA of Streptococcus pneumoniae and their interaction with human endothelial and red blood cells

Streptococcus pneumoniae is a Gram-positive opportunistic pathogen that can colonize the upper respiratory tract. It is a leading cause of a wide range of infectious diseases, including community-acquired pneumonia and meningitis. Pneumococcal infections cause 1-2 million deaths per year, most of which occur in developing countries. Here, we focused on three choline-binding proteins (CBPs), i.e., PspC, PspA, and LytA. These pneumococcal proteins have different surface-exposed regions but share related choline-binding anchors. These surface-exposed pneumococcal proteins are in direct contact with host cells and have diverse functions. We explored the role of the three CBPs on adhesion and pathogenicity in a human host by performing relevant imaging and functional analyses, such as electron microscopy, confocal laser scanning microscopy, and functional quantitative assays, targeting biofilm formation and the hemolytic capacity of S. pneumoniae. In vitro biofilm formation assays and electron microscopy experiments were used to examine the ability of knockout mutant strains lacking the lytA, pspC, or pspA genes to adhere to surfaces. We found that LytA plays an important role in robust synthesis of the biofilm matrix. PspA and PspC appeared crucial for the hemolytic effects of S. pneumoniae on human red blood cells. Furthermore, all knockout mutants caused less damage to endothelial cells than wild-type bacteria, highlighting the significance of each CPB for the overall pathogenicity of S. pneumoniae. Hence, in addition to their structural function within the cell wall of S. pneumoniae, each of these three surface-exposed CBPs controls or mediates multiple steps during bacterial pathogenesis.

Probing the binding nature and stability of highly transmissible mutated variant alpha to omicron of SARS-CoV-2 RBD with ACE2 via molecular dynamics simulation

Currently, no approved drug is available as a causative agent of coronavirus disease 2019 (COVID-19) except for some repurposed drugs. The first structure of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was reported in late 2019, based on that some vaccines and repurposed drugs were approved to prevent people from COVID-19 during the pandemic situation. Since then, new types of variants emerged and notably, the receptor binding domain (RBD) adopted different binding modes with angiotensin-converting enzyme 2 (ACE2); this made significant changes in the progression of COVID-19. Some of the new variants are highly infectious spreading fast and dangerous. The present study is focused on understanding the binding mode of the RBD of different mutated SARS-CoV-2 variants of concern (alpha to omicron) with the human ACE2 using molecular dynamics simulation. Notably, some variants adopted a new binding mode of RBD with ACE2 and formed different interactions, which is unlike the wild type; this was confirmed from the comparison of interaction between RBD-ACE2 of all variants with its wild-type structure. Binding energy values confirm that some mutated variants exhibit high binding affinity. These findings demonstrate that the variations in the sequence of SARS-CoV-2 S-protein altered the binding mode of RBD; this may be the reason that the virus has high transmissibility and causes new infections. This in-silico study on mutated variants of SARS-CoV-2 RBD with ACE2 insights into their binding mode, binding affinity, and stability. This information may help to understand the RBD-ACE2 binding domains, which allows for designing newer drugs and vaccines.

Pneumococcal Choline-Binding Proteins Involved in Virulence as Vaccine Candidates

Streptococcus pneumoniae is a pathogen responsible for millions of deaths worldwide. Currently, the available vaccines for the prevention of S. pneumoniae infections are the 23-valent pneumococcal polysaccharide-based vaccine (PPV-23) and the pneumococcal conjugate vaccines (PCV10 and PCV13). These vaccines only cover some pneumococcal serotypes (up to 100 different serotypes have been identified) and are unable to protect against non-vaccine serotypes and non-encapsulated pneumococci. The emergence of antibiotic-resistant non-vaccine serotypes after these vaccines is an increasing threat. Therefore, there is an urgent need to develop new pneumococcal vaccines which could cover a wide range of serotypes. One of the vaccines most characterized as a prophylactic alternative to current PPV-23 or PCVs is a vaccine based on pneumococcal protein antigens. The choline-binding proteins (CBP) are found in all pneumococcal strains, giving them the characteristic to be potential vaccine candidates as they may protect against different serotypes. In this review, we have focused the attention on different CBPs as vaccine candidates because they are involved in the pathogenesis process, confirming their immunogenicity and protection against pneumococcal infection. The review summarizes the major contribution of these proteins to virulence and reinforces the fact that antibodies elicited against many of them may block or interfere with their role in the infection process.