BLUE WATERS ANNUAL REPORT 2019

GA HOW BLUE WATERS IS AIDING THE FIGHT AGAINST Allocation: Illinois/520 Knh PI: Rafael C. Bernardi1 TN 2 Collaborator: Hermann E. Gaub

1University of Illinois at Urbana–Champaign 2Ludwig–Maximilians–Universität BW EXECUTIVE SUMMARY to investigate with exquisite precision the mechanics of interac- Owing to their high occurrence in ever more common hos- tion between SdrG and Fgβ. SdrG is an SD-repeat G and pital-acquired , studying the mechanisms of is one of the adhesin of Staphylococcus epidermidis. Fgβ by Staphylococcus epidermidis and Staphylococcus aureus is of is the human fibrinogen β and is a short peptide that is part of broad interest. These can frequently form biofilms on the human extracellular matrix. implants and medical devices and are commonly involved in sep- For SMD molecular dynamics simulations, the team uses Blue sis—the human body’s often deadly response to infections. Waters’ GPU nodes (XK) and the GPU-accelerated NAMD pack- Central to the formation of biofilms is very close interaction age. In a wide-sampling strategy, the team carried out hundreds between microbial surface proteins called adhesins and compo- of SMD runs for a total of over 50 microseconds of simulation. nents of the extracellular matrix of the host. The research team To characterize the coupling between the bacterial SdrG pro- uses Blue Waters to explore how the bond between staphylococ- tein and the Fgβ peptide, the team conducts SMD simulations cal adhesin and its human target can withstand forces that so far with constant velocity stretching at multiple pulling speeds. The BI have only been seen in covalent bonds. The team uses a syner- SMD procedure is inspired by experimental approaches and is gistic combination of computational and experimental methods. equivalent to attaching one end of a harmonic spring to the end This approach is essential to elucidating the mechanism by which of a SdrG protein and pulling on the Fgβ peptide. To quantify an intricate network of hydrogen bonds makes the staphylococ- the strength of interaction between the two molecules, the force cal adhesion ultrastable, revealing possible routes for the devel- applied to the harmonic spring is recorded at regular intervals. opment of antimicrobial strategies. RESULTS & IMPACT RESEARCH CHALLENGE The steered molecular dynamics simulations performed on are increasingly powerless against a growing num- Blue Waters revealed, and single-molecule force spectroscopy ber of “super ” that have evolved to survive humankind’s experiments confirmed, the mechanism by which this complex pharmacological offensive. The shortage of new medicines to treat withstands forces previously only associated with the strength of what the U.S. Centers for Disease Control calls “nightmare bac- a covalent bond. The target human peptide (Fgβ), confined in a Figure 1: Staph bacteria (shown as colorful rods) adhere to their human hosts (surface at the bottom) with exceptional mechanical resilience. By combining experimental teria” is evident. Public health agencies across the world have be- screwlike manner in the binding pocket of the bacterial adhesin and computational approaches, the research team is deciphering the physical mechanisms that underlie the persistent stickiness of these bacterial adhesins (translucent gun warning of the consequences of a postantibiotic era in which protein (SdrG), distributes forces mainly toward the peptide back- purple structures), a major step in combating such invaders. a common infection could, once again, become a death sentence. bone through an intricate hydrogen bond network. This behavior The fight against sepsis, the human body’s often deadly re- allows SdrG to attach to Fgβ with exceptionally resilient mech- WHY BLUE WATERS sponse to bacterial infections, has become the topic of nation- anostability, virtually independent of the peptide’s side chains. The research group’s work depends on obtaining multiple sim- wide campaigns in the United States. Exploring the mechanism This unexpected mechanism expands the understanding of why ulation replicas with a fast turnaround time. This approach al- by which bacteria initiate infections is, therefore, key to devel- adhesion is so resilient, which may open new ways to lows the team to quickly test any and all hypotheses both compu- oping new antimicrobial therapies. Investigations at the molec- inhibit staphylococcal invasion. The development of anti-adhe- tationally and experimentally. For this work, the team uses Blue ular level of the mechanism of adhesion between Staphylococ- sion therapy could block the first steps of biofilm formation by Waters GPU (XK) nodes and CUDA-accelerated molecular dy- cus epidermidis and Staphylococcus aureus and the extracellular staph bacteria, facilitating bacterial clearance. Understanding the namics software NAMD. matrix of their human hosts could lead to a detailed understand- mechanism of staph infection at the atomic level may also open ing of adhesion, one of the first steps of staph infections. This -un new avenues for an intelligent design of antimicrobial therapies. derstanding may, in turn, allow researchers to develop possible The research team’s initial findings were published inScience competitors for their interaction with humans, stopping infec- in 2018 [1]. Currently, the team is working on developing a new tion at its early stages. protocol for finding peptides with a higher affinity for staphylo- coccal adhesins. The initial results are promising, and a peptide METHODS & CODES sequence with a slightly higher affinity has already been identified. The research uses single-molecule force spectroscopy along with all-atom steered molecular dynamics (SMD) simulations

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