Molecular Basis of Ca(II)-Induced Tetramerization and Transition-Metal Sequestration in Human Calprotectin.

Human calprotectin (CP, S100A8/S100A9 oligomer, MRP8/MRP14 oligomer) is an abundant innate immune protein that contributes to the host metal-withholding response. Its ability to sequester transition metal nutrients from microbial pathogens depends on a complex interplay of Ca(II) binding and self-association, which converts the αβ heterodimeric apo protein into a Ca(II)-bound (αβ) heterotetramer that displays enhanced transition metal affinities, antimicrobial activity, and protease stability. A paucity of structural data on the αβ heterodimer has hampered molecular understanding of how Ca(II) binding enables CP to exert its metal-sequestering innate immune function.

Calcium Binding to the Innate Immune Protein Human Calprotectin Revealed by Integrated Mass Spectrometry.

Although knowledge of the coordination chemistry and metal-withholding function of the innate immune protein human calprotectin (hCP) has broadened in recent years, understanding of its Ca-binding properties in solution remains incomplete. In particular, the molecular basis by which Ca binding affects structure and enhances the functional properties of this remarkable transition-metal-sequestering protein has remained enigmatic. To achieve a molecular picture of how Ca binding triggers hCP oligomerization, increases protease stability, and enhances antimicrobial activity, we implemented a new integrated mass spectrometry (MS)-based approach that can be readily generalized to study other protein-metal and protein-ligand interactions.

Exosome swarms eliminate airway pathogens and provide passive epithelial immunoprotection through nitric oxide.

Background: Nasal mucosa-derived exosomes (NMDEs) harbor immunodefensive proteins and are capable of rapid interepithelial protein transfer.

Objectives: We sought to determine whether mucosal exposure to inhaled pathogens stimulates a defensive swarm of microbiocidal exosomes, which also donate their antimicrobial cargo to adjacent epithelial cells.

Methods: We performed an institutional review board-approved study of healthy NMDE secretion after Toll-like receptor (TLR) 4 stimulation by LPS (12.

Oxidative Post-translational Modifications Accelerate Proteolytic Degradation of Calprotectin.

Oxidative post-translational modifications affect the structure and function of many biomolecules. Herein we examine the biophysical and functional consequences of oxidative post-translational modifications to human calprotectin (CP, S100A8/S100A9 oligomer, MRP8/MRP14 oligomer, calgranulins A/B oligomer). This abundant metal-sequestering protein contributes to innate immunity by starving invading microbial pathogens of transition metal nutrients in the extracellular space.

The Hexahistidine Motif of Host-Defense Protein Human Calprotectin Contributes to Zinc Withholding and Its Functional Versatility.

Human calprotectin (CP, S100A8/S100A9 oligomer, MRP-8/MRP-14 oligomer) is an abundant host-defense protein that is involved in the metal-withholding innate immune response. CP coordinates a variety of divalent first-row transition metal ions, which is implicated in its antimicrobial function, and its ability to sequester nutrient Zn(II) ions from microbial pathogens has been recognized for over two decades. CP has two distinct transition-metal-binding sites formed at the S100A8/S100A9 dimer interface, including a histidine-rich site composed of S100A8 residues His17 and His27 and S100A9 residues His91 and His95.

Calcium-induced Tetramerization and Zinc Chelation Shield Human Calprotectin from Degradation by Host and Bacterial Extracellular Proteases.

Calprotectin (CP, S100A8/S100A9 oligomer, MRP-8/14 oligomer, calgranulins A and B) is a protein component of the innate immune system that contributes to the metal-withholding response by sequestering bioavailable transition metal ions at sites of infection. Human CP employs Ca(II) ions to modulate its quaternary structure, transition metal binding properties, and antimicrobial activity. In this work, we report the discovery that Ca(II)-induced self-association of human CP to afford heterotetramers protects the protein scaffold from degradation by host serine proteases.

Rapid formal hydrolysis of peptide-αthioesters.

In the presence of 2-mercaptoethanol peptide-(α)thioesters undergo smooth conversion to their corresponding peptide-(α)carboxylates. This general and operationally simple reaction extends the utility of a promising new strategy for cleaving resin-bound Boc/benzyl-protected peptides without the use of hydrogen fluoride.