Structure of von Willebrand factor A1 on polystyrene determined from experimental and calculated sum frequency generation spectra

Hydrophobic Polystyrene-Modified Gelatin Enhances Fast Hemostasis and Tissue Regeneration in Traumatic Brain Injury

Hemostatic sealant is required to deal with blood loss, especially in the scenario of traumatic brain injury (TBI), which presents high rates of morbidity and disability. Hemostasis in surgery with traditional gelatin-based sealants often leads to blood loss and other issues in brain because of the hydrophilic gelatin swelling. Herein, hydrophobic effects on the hemostasis in TBI surgery are studied by tuning the chain length of polystyrene (PS) onto methylacrylated gelatin (Gel-MA). The hydrophobicity and hemostatic efficiency can be tuned by controlling the length of PS groups. The platelet activation of modified sealants Gel-MA-2P, Gel-MA-P, and Gel-MA-0.5P is as much as 17.5, 9.1, and 2.1 times higher than Gel-MA in vitro. The hemostatic time of Gel-MA-2P, Gel-MA-P, and Gel-MA-0.5P groups is 2.0-, 1.6-, and 1.1-folds faster than that in Gel-MA group in TBI mice. Increased formation of fibrins and platelet aggregation can also be observed in vitro by scanning electron microscopy. Animal's mortality is lowered by 46%, neurologic deficiency is reduced by 1.5 times, and brain edema is attenuated by 10%. Protein expression is further investigated to exhibit toxic iron-related processes caused by delayed hemostasis and activation of platelets via PI3K/PKC-α signaling. The hydrophobic Gel-MA has the potential in hemostatic TBI and promotes nervous system recovery in brain with the potentials in clinics.

Crowding alters F-actin secondary structure and hydration

Actin, an important component of eukaryotic cell cytoskeleton, regulates cell shape and transport. The morphology and biochemical properties of actin filaments are determined by their structure and protein-protein contacts. Crowded environments can organize filaments into bundles, but less is known about how they affect F-actin structure. This study used 2D IR spectroscopy and spectral calculations to examine how crowding and bundling impact the secondary structure and local environments in filaments and weakly or strongly bundled networks. The results reveal that bundling induces changes in actin's secondary structure, leading to a decrease in β-sheet and an increase in loop conformations. Strongly bundled networks exhibit a decrease in backbone solvent exposure, with less perturbed α-helices and nearly "locked" β-sheets. Similarly, the loops become less hydrated but maintain a dynamic environment. These findings highlight the role of loop structure in actin network morphology and stability under morphology control by PEG.

Interaction of Amyloid-β-(1-42) Peptide and Its Aggregates with Lipid/Water Interfaces Probed by Vibrational Sum-Frequency Generation Spectroscopy

In this study, we use surface-sensitive vibrational sum-frequency generation (VSFG) spectroscopy to investigate the interaction between model lipid monolayers and Aβ(1-42) in its monomeric and aggregated states. Combining VSFG with atomic force microscopy (AFM) and thioflavin T (ThT) fluorescence measurements, we found that only small aggregates with probably a β-hairpin-like structure adsorbed to the zwitterionic lipid monolayer (DOPC). In contrast, larger aggregates with an extended β-sheet structure adsorbed to a negatively charged lipid monolayer (DOPG). The adsorption of small, initially formed aggregates strongly destabilized both monolayers, but only the DOPC monolayer was completely disrupted. We showed that the intensity of the amide-II' band in achiral (SSP) and chiral (SPP) polarization combinations increased in time when Aβ(1-42) aggregates accumulated at the DOPG monolayer. Nevertheless, almost no adsorption of preformed mature fibrils to DOPG monolayers was detected. By performing spectral VSFG calculations, we revealed a clear correlation between the amide-II' signal and the degree of amyloid aggregates (e.g., oligomers or (proto)fibrils) of various Aβ(1-42) structures. The calculations showed that only structures with a significant amyloid β-sheet content have a strong amide-II' intensity, in line with previous Raman studies. The combination of the presented results substantiates the amide-II(') band as a legitimate amyloid marker.

Backbone Structure of Diatom Silaffin Peptide R5 in Biosilica Determined by Combining Solid-State NMR with Theoretical Sum-Frequency Generation Spectra

Silaffin peptide R5 is key for the biogenesis of silica cell walls of diatoms. Biosilification by the R5 peptide has potential in biotechnology, drug development, and materials science due to its ability to precipitate stable, high fidelity silica sheets and particles. A true barrier for the design of novel peptide-based architectures for wider applications has been the limited understanding of the interfacial structure of R5 when precipitating silica nanoparticles. While R5-silica interactions have been studied in detail at flat surfaces, the structure within nanophase particles is still being debated. We herein elucidate the conformation of R5 in its active form within silica particles by combining interface-specific vibrational spectroscopy data with solid-state NMR torsion angles using theoretical spectra. Our calculations show that R5 is structured and undergoes a conformational transition from a strand-type motif in solution to a more curved, contracted structure when interacting with silica precursors.

Developments and Ongoing Challenges for Analysis of Surface-Bound Proteins

Proteins at surfaces and interfaces play important roles in the function and performance of materials in applications ranging from diagnostic assays to biomedical devices. To improve the performance of these materials, detailed molecular structure (conformation and orientation) along with the identity and concentrations of the surface-bound proteins on those materials must be determined. This article describes radiolabeling, surface plasmon resonance, quartz crystal microbalance with dissipation, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, sum frequency generation spectroscopy, and computational techniques along with the information each technique provides for characterizing protein films. A multitechnique approach using both experimental and computation methods is required for these investigations. Although it is now possible to gain much insight into the structure of surface-bound proteins, it is still not possible to obtain the same level of structural detail about proteins on surfaces as can be obtained about proteins in crystals and solutions, especially for large, complex proteins. However, recent results have shown it is possible to obtain detailed structural information (e.g., backbone and side chain orientation) about small peptides (5-20 amino sequences) on surfaces. Current studies are extending these investigations to small proteins such as protein G B1 (∼6 kDa). Approaches for furthering the capabilities for characterizing the molecular structure of surface-bound proteins are proposed.

Unsaturated Lipid Accelerates Formation of Oligomeric β-Sheet Structure of GP41 Fusion Peptide in Model Cell Membrane

Membrane fusion of the viral and host cell membranes is the initial step of virus infection and is catalyzed by fusion peptides. Although the β-sheet structure of fusion peptides has been proposed to be the most important fusion-active conformation, it is still very challenging to experimentally identify different types of β-sheet structures at the cell membrane surface in situ and in real time. In this work, we demonstrate that the interface-sensitive amide II spectral signals of protein backbones, generated by the sum frequency generation vibrational spectroscopy, provide a sensitive probe for directly capturing the formation of oligomeric β-sheet structure of fusion peptides. Using human immunodeficiency virus (HIV) glycoprotein GP41 fusing peptide (FP23) as the model, we find that formation speed of oligomeric β-sheet structure depends on lipid unsaturation. The unsaturated lipid such as POPG can accelerate formation of oligomeric β-sheet structure of FP23. The β-sheet structure is more deeply inserted into the hydrophobic region of the POPG bilayer than the α-helical segment. This work will pave the way for future researches on capturing intermediate structures during membrane fusion processes and revealing the fusion mechanism.

Acidic Environment Significantly Alters Aggregation Pathway of Human Islet Amyloid Polypeptide at Negative Lipid Membrane

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) at cell membrane has a close relationship with the development of type 2 diabetes (T2DM). This aggregation process is susceptible to various physiologically related factors, and systematic studies on condition-mediated hIAPP aggregation are therefore essential for a thorough understanding of the pathology of T2DM. In this study, we combined surface-sensitive amide I and amide II spectral signals from the protein backbone, generated simultaneously in a highly sensitive femtosecond broad-band sum frequency generation vibrational spectroscopy system, to examine the effect of environmental pH on the dynamical structural changes of hIAPP at membrane surface in situ and in real time. Such a combination can directly discriminate the formation of β-hairpin-like monomer and oligomer/fibril at the membrane surface. It is evident that, in an acidic milieu, hIAPP slows down its conformational evolution and alters its aggregation pathway, leading to the formation of off-pathway oligomers. When matured hIAPP aggregates are exposed to basic subphase, partial conversion from β-sheet oligomers into ordered β-sheet fibrillar structures is observed. When exposed to acidic environment, however, hIAPP fibrils partially converse into more loosely patterned β-sheet oligomeric structures.

Otoferlin C2F Domain-Induced Changes in Membrane Structure Observed by Sum Frequency Generation

Proteins that contain C2 domains are involved in a variety of biological processes, including encoding of sound, cell signaling, and cell membrane repair. Of particular importance is the interface activity of the C-terminal C2F domain of otoferlin due to the pathological mutations known to significantly disrupt the protein's lipid membrane interface binding activity, resulting in hearing loss. Therefore, there is a critical need to define the geometry and positions of functionally important sites and structures at the otoferlin-lipid membrane interface. Here, we describe the first in situ probe of the protein orientation of otoferlin's C2F domain interacting with a cell membrane surface. To identify this protein's orientation at the lipid interface, we applied sum frequency generation (SFG) vibrational spectroscopy and coupled it with simulated SFG spectra to observe and quantify the otoferlin C2F domain interacting with model lipid membranes. A model cell membrane was built with equal amounts of phosphatidylserine and phosphatidylcholine. SFG measurements of the lipids that make up the model membrane indicate a 62% increase in amplitude from the SFG signal near 2075 cm^-1 upon protein interaction, suggesting domain-induced changes in the orientation of the lipids and possible membrane curvature. This increase is related to lipid ordering caused by the docking interaction of the otoferlin C2F domain. SFG spectra taken from the amide-I region contain features near 1630 and 1670 cm^-1 related to the C2F domains beta-sandwich secondary structure, thus indicating that the domain binds in a specific orientation. By mapping the simulated SFG spectra to the experimentally collected SFG spectra, we found the C2F domain of otoferlin orients 22° normal to the lipid surface. This information allows us to map what portion of the domain directly interacts with the lipid membrane.