Biology subjects

Roeters, S. J.

Publications and source records attributed to Roeters, S. J..

3 recordsLinked to original sources

bioRxiv2022

In situ identification of secondary structures in unpurified Bombyx mori silk fibrils using polarized two-dimensional infrared spectroscopy

The mechanical properties of biomaterials are dictated by the interactions and conformations of their building blocks, typically proteins. Although the macroscopic behaviour of biomaterials is widely studied, our understanding of the underlying molecular properties is generally limited. Among the non-invasive and label-free methods to investigate molecular structures, infrared spectroscopy is one of the most commonly used tools, because the absorption bands of the amide groups strongly depend on protein secondary structure. However, spectral congestion usually complicates the analysis of the amide spectrum. Here, we apply polarized two-dimensional (2D) infrared spectroscopy (IR) to directly identify the protein secondary structures in native silk filks cast from Bombyx mori silk feedstock. Without any additional analysis, such as peak fitting, we find that the initial effect of hydration is an increase of the random-coil content at the expense of the -helix content, while the {beta}-sheet content is unchanged, and only increases at a later stage. This paper demonstrates that 2D-IR can be a valuable tool for characterizing biomaterials.

biophysics↗

bioRxiv2021

The giant Staphylococcus epidermidis surface protein Embp binds selectively to fibrillated fibronectin through a Velcro-like mechanism

Staphylococcus epidermidis causes some of the most hard-to-treat clinical infections by forming biofilms: Multicellular communities of bacteria encased in a protective matrix, supporting immune evasion and tolerance against antibiotics. Biofilms occur most commonly on medical implants, and a key event in implant colonization is the robust adherence to the surface, facilitated by interactions between bacterial surface proteins and host matrix components. S. epidermidis is equipped with a giant adhesive protein, Embp, which facilitates bacterial interactions with surface-deposited, but not soluble fibronectin. The structural basis behind this selective binding process has remained obscure. Using a suite of single-cell and single-molecule analysis techniques, we show that S. epidermidis is capable of such distinction because Embp binds specifically to fibrillated fibronectin on surfaces, while ignoring globular fibronectin in solution. S. epidermidis adherence is critically dependent on multi-valent interactions involving 50 fibronectin-binding repeats of Embp. This unusual, Velcro-like interaction proved critical for colonization of surfaces under high flow, making this newly identified attachment mechanism particularly relevant for colonization of intravascular devices, such as prosthetic heart valves or vascular grafts. Other biofilm-forming pathogens, such as Staphylococcus aureus, express homologs of Embp and likely deploy the same mechanism for surface colonization. Our results may open for a novel direction in efforts to combat devastating, biofilm-associated infections, as the development of implant materials that steer the conformation of adsorbed proteins is a much more manageable task than avoiding protein adsorption altogether. Graphical abstractFibronectin exists in two different conformations in the body. It circulates in the bodily fluids in globular conformation, however, it become fibrillated once adsorbed to an implant surface. S. epidermidis possess a giant 1 MDa receptor known as Embp bind specifically to fibrillated Fn but not to the globular Fn. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/446437v2_ufig1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@1999895org.highwire.dtl.DTLVardef@f0717corg.highwire.dtl.DTLVardef@1aa8773org.highwire.dtl.DTLVardef@a2991b_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2020

The Ice Nucleating Protein InaZ is Activated by Low Temperature

Ice-nucleation active (INA) bacteria can promote the growth of ice more effectively than any other known material. Utilizing specialized ice-nucleating proteins (INPros), they obtain nutrients from plants by inducing frost damage and, when airborne in the atmosphere, they drive ice nucleation within clouds and may affect global precipitation patterns. Despite their evident environmental importance, the molecular mechanisms behind INPro-induced freezing have remained largely elusive. In the present study, we investigated the folding and the structural basis for interactions between water and the ice-nucleating protein InaZ from the INA bacterium Pseudomonas syringae strain R10.79. Using vibrational sum-frequency generation and two-dimensional infrared spectroscopy, we demonstrate that the ice-active repeats of InaZ adopt a {beta}-helical structure in solution and at water surfaces. In this configuration, hydrogen bonding between INPros and water molecules imposes structural ordering on the adjacent water network. The observed order of water increases as the interface is cooled to temperatures close to the melting point of water. Experimental SFG data combined with spectral calculations and molecular-dynamics simulations shows that the INPro reorients at lower temperatures. We suggest that the reorientation can enhance order-inducing water interactions and, thereby, the effectiveness of ice nucleation by InaZ.

biophysics↗