Headless C1q: a new molecular tool to decipher its collagen-like functions

Beyond the Triple Helix: Exploration of the Hierarchical Assembly Space of Collagen-like Peptides

The de novo design of self-assembling peptides has garnered significant attention in scientific research. While alpha-helical assemblies have been extensively studied, exploration of polyproline type II (PPII) helices, such as those found in collagen, remains relatively limited. In this study, we focused on understanding the sequence-structure relationship in hierarchical assemblies of collagen-like peptides, using defense collagen SP-A as a model. By dissecting the sequence derived from SP-A and synthesizing short collagen-like peptides, we successfully constructed a discrete bundle of hollow triple helices. Mutation studies pinpointed amino acid sequences, including hydrophobic and charged residues that are critical for oligomer formation. These insights guided the de novo design of collagen-like peptides, resulting in the formation of diverse quaternary structures, including discrete and heterogenous bundled oligomers, 2D nanosheets, and pH-responsive nanoribbons. Our study represents a significant advancement in the understanding and harnessing of collagen higher-order assemblies beyond the triple helix.

A recombinant technique for mapping functional sites of heterotrimeric collagen helices: Collagen IV CB3 fragment as a prototype for integrin binding

Collagen superfamily of proteins is a major component of the extracellular matrix. Defects in collagens underlie the cause of nearly 40 human genetic diseases in millions of people worldwide. Pathogenesis typically involves genetic alterations of the triple helix, a hallmark structural feature that bestows exceptional mechanical resistance to tensile forces and a capacity to bind a plethora of macromolecules. Yet, there is a paramount knowledge gap in understanding the functionality of distinct sites along the triple helix. Here, we present a recombinant technique to produce triple helical fragments for functional studies. The experimental strategy utilizes the unique capacity of the NC2 heterotrimerization domain of collagen IX to drive three α-chain selection and registering the triple helix stagger. For proof of principle, we produced and characterized long triple helical fragments of collagen IV that were expressed in a mammalian system. The heterotrimeric fragments encompassed the CB3 trimeric peptide of collagen IV, which harbors the binding motifs for α1β1 and α2β1 integrins. Fragments were characterized and shown to have a stable triple helix, post-translational modifications, and high affinity and specific binding of integrins. The NC2 technique is a universal tool for the high-yield production of heterotrimeric fragments of collagens. Fragments are suitable for mapping functional sites, determining coding sequences of binding sites, elucidating pathogenicity and pathogenic mechanisms of genetic mutations, and production of fragments for protein replacement therapy.

Serum Proteomic Signatures in Umbilical Cord Blood of Preterm Neonates Delivered by Women with Gestational Diabetes

Background

Women who develop diabetes during pregnancy are at higher risk of preterm birth. Here, we identified differentially expressed proteins (DEPs) in the serum of umbilical cord blood samples obtained from preterm neonates delivered by women with gestational diabetes to provide therapeutic targets for clinical drug development.

Materials and Methods

Umbilical cord blood was collected after delivery of preterm neonates by women with gestational diabetes and after delivery of healthy neonates by women without diabetes. DEPs in the serum samples were identified using liquid chromatography-tandem mass spectrometry. Gene Ontology (GO), cluster analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to determine the biological functions associated with these DEPs. Enzyme linked immunosorbent assay was used to confirm the key DEPs.

Results

We found that 21 proteins were significantly upregulated, and 51 proteins were significantly downregulated in 72 DEPs in serum samples. GO analyses showed that the DEPs were mainly associated with the GO terms cellular process, biological regulation, cellular anatomical entity, and binding. KEGG signaling pathway analysis indicated that most of the upregulated DEPs were associated with the complement and coagulation cascades, Staphylococcus aureus infection, pertussis, HIF-1 signaling pathway and PPAR signaling pathway and that most of the downregulated DEPs were associated with the complement and coagulation cascades, dilated cardiomyopathy, pathways in cancer, Chagas disease, and hypertrophic cardiomyopathy. The results of KEGG pathway annotation and enrichment analyses indicated that changes in the complement and coagulation cascades may be importantly associated with preterm delivery of neonates by women with gestational diabetes. The key DEPs were confirmed by enzyme linked immunosorbent assay.

Conclusion

Our proteomics and bioinformatics analyses identified several key proteins and the complement and coagulation cascades pathway that warrant further investigation as potential novel therapeutic targets in preterm delivery among women with gestational diabetes.

Hollow Octadecameric Self-Assembly of Collagen-like Peptides

The folding of collagen is a hierarchical process that starts with three peptides associating into the characteristic triple helical fold. Depending on the specific collagen in question, these triple helices then assemble into bundles reminiscent of α-helical coiled-coils. Unlike α-helices, however, the bundling of collagen triple helices is very poorly understood with almost no direct experimental data available. In order to shed light on this critical step of collagen hierarchical assembly, we have examined the collagenous region of complement component 1q. Thirteen synthetic peptides were prepared to dissect the critical regions allowing for its octadecameric self-assembly. We find that short peptides (under 40 amino acids) are able to self-assemble into specific (ABC)6 octadecamers. This requires the ABC heterotrimeric composition as the self-assembly subunit, but does not require disulfide bonds. Self-assembly into this octadecamer is aided by short noncollagenous sequences at the N-terminus, although they are not entirely required. The mechanism of self-assembly appears to begin with the very slow formation of the ABC heterotrimeric helix, followed by rapid bundling of triple helices into progressively larger oligomers, terminating in the formation of the (ABC)6 octadecamer. Cryo-electron microscopy reveals the (ABC)6 assembly as a remarkable, hollow, crown-like structure with an open channel approximately 18 Å at the narrow end and 30 Å at the wide end. This work helps to illuminate the structure and assembly mechanism of a critical protein in the innate immune system and lays the groundwork for the de novo design of higher order collagen mimetic peptide assemblies.

Recombinant protein polymer-antibody conjugates for applications in nanotechnology and biomedicine

Currently, there are over 100 antibody-based therapeutics on the market for the treatment of various diseases. The increasing importance of antibody treatment is further highlighted by the recent FDA emergency use authorization of certain antibody therapies for COVID-19 treatment. Protein-based materials have gained momentum for antibody delivery due to their biocompatibility, tunable chemistry, monodispersity, and straightforward synthesis and purification. In this review, we discuss progress in engineering the molecular features of protein-based biomaterials, in particular recombinant protein polymers, for introducing novel functionalities and enhancing the delivery properties of antibodies and related binding protein domains.

Cation-π Interactions and Their Role in Assembling Collagen Triple Helices

Cation-π interactions play a significant role in the stabilization of globular proteins. However, their role in collagen triple helices is less well understood and they have rarely been used in de novo designed collagen mimetic systems. In this study, we analyze the stabilizing and destabilizing effects in pairwise amino acid interactions between cationic and aromatic residues in both axial and lateral sequential relationships. Thermal unfolding experiments demonstrated that only axial pairs are stabilizing, while the lateral pairs are uniformly destabilizing. Molecular dynamics simulations show that pairs with an axial relationship can achieve a near-ideal interaction distance, but pairs in a lateral relationship do not. Arginine-π systems were found to be more stabilizing than lysine-π and histidine-π. Arginine-π interactions were then studied in more chemically diverse ABC-type heterotrimeric helices, where arginine-tyrosine pairs were found to form the best helix. This work helps elucidate the role of cation-π interactions in triple helices and illustrates their utility in designing collagen mimetic peptides.

Understanding the contextual functions of C1q and LAIR-1 and their applications

The importance of the complement component C1q has been highlighted by its involvement in autoimmunity, infection, inflammatory diseases, and tumors. The unique tulip-like structure of C1q has both a collagen-like stalk (C1q tail) and heterotrimeric globular head (gC1q), each with different binding specificities, and the binding of these components to their respective receptors leads to functional complexities in the body and bridges innate and adaptive immunity. This review describes the fundamental roles of C1q in various microenvironments and focuses on the importance of the interactions of C1q and its receptors with the inhibitory receptor LAIR-1 in maintaining homeostasis. Current therapeutic opportunities modulating LAIR-1 are also discussed.

Research into the activities of the protein C1q, involved in a cascade of molecular interactions of the immune response called complement activation, is revealing new details of the protein’s role and opening up possible new therapeutic opportunities. Myoungsun Son at Feinstein Institutes for Medical Research in Manhasset, USA, reviews the involvement of C1q in infection, autoimmunity, inflammatory diseases and tumors. The interaction of C1q with a receptor protein called LAIR-1 seems to be particularly significant. LAIR-1 is present in the membrane of most blood-forming cells and is involved in maintaining the healthy balance of cellular activities referred to as homeostasis. Emerging research suggests that targeting the interactions between C1q and LAIR-1 could enable the development of new treatments for many diseases, including inflammatory diseases, the autoimmune condition lupus, a variety of cancers, and possibly Covid-19.

Scattering-based Light Microscopy: From Metal Nanoparticles to Single Proteins

Our ability to detect, image, and quantify nanoscopic objects and molecules with visible light has undergone dramatic improvements over the past few decades. While fluorescence has historically been the go-to contrast mechanism for ultrasensitive light microscopy due to its superior background suppression and specificity, recent developments based on light scattering have reached single-molecule sensitivity. They also have the advantages of universal applicability and the ability to obtain information about the species of interest beyond its presence and location. Many of the recent advances are driven by novel approaches to illumination, detection, and background suppression, all aimed at isolating and maximizing the signal of interest. Here, we review these developments grouped according to the basic principles used, namely darkfield imaging, interferometric detection, and surface plasmon resonance microscopy.

Molecular Basis of Complement C1q Collagen-Like Region Interaction with the Immunoglobulin-Like Receptor LAIR-1

The immune system homeostasis relies on a tight equilibrium of interconnected stimulatory and inhibitory signals. Disruption of this balance is characteristic of autoimmune diseases such as systemic lupus erythematosus (SLE). Aside from activating the classical complement pathway and enhancing pathogens and apoptotic cells phagocytosis, C1q has been recently shown to play an important role in immune modulation and tolerance by interacting with several inhibitory and stimulatory immune receptors. Due to its functional organization into collagen-like (CLR) and globular (GR) regions and its multimeric nature, C1q is able to interact simultaneously with several of these receptors and locally congregate pro- and anti-inflammatory signals, thus modulating the immune response. Leukocyte associated immunoglobulin-like (Ig-like) receptor 1 (LAIR-1), a ubiquitous collagen receptor expressed in many immune cell types, has been reported to interact with the CLR of C1q. In this study, we provide new insights into the molecular and structural determinants underlying C1q/LAIR-1 interaction. Recombinant LAIR-1 extracellular Ig-like domain was produced and tested for its interaction with C1q. A molecular dissection of C1q combined with competition assays reveals that LAIR-1 interacts with C1q’s CLR through a binding site close but different from the one of its associated C1r2s2 proteases tetramer. On the other side, we identified LAIR-1 residues involved in C1q interaction by site-directed mutational analysis. All together, these results lead to propose a possible model for C1q interaction with LAIR-1 and will contribute to the fundamental understanding of C1q-mediated immune tolerance.