The Biophysical Interaction of the Danger-Associated Molecular Pattern (DAMP) Calreticulin with the Pattern-Associated Molecular Pattern (PAMP) Lipopolysaccharide

Abstract

The endoplasmic reticulum (ER) chaperone protein, calreticulin (CRT), is essential for proper glycoprotein folding and maintaining cellular calcium homeostasis. During ER stress, CRT is overexpressed as part of the unfolded protein response (UPR). In addition, CRT can be released as a damage-associated molecular pattern (DAMP) molecule that may interact with pathogen-associated molecular patterns (PAMPs) during the innate immune response. One such PAMP is lipopolysaccharide (LPS), a component of the gram-negative bacterial cell wall. In this report, we show that recombinant and native human placental CRT strongly interacts with LPS in solution, solid phase, and the surface of gram-negative and gram-positive bacteria. Furthermore, LPS induces oilgomerization of CRT with a disappearance of the monomeric form. The application of recombinant CRT (rCRT) to size exclusion and anion exchange chromatography shows an atypical heterogeneous elution profile, indicating that LPS affects the conformation and ionic charge of CRT. Interestingly, LPS bound to CRT is detected in sera of bronchiectasis patients with chronic bacterial infections. By ELISA, rCRT dose-dependently bound to solid phase LPS via the N- and C-domain globular head region of CRT and the C-domain alone. The specific interaction of CRT with LPS may be important in PAMP innate immunity.

Calreticulin and Galectin-3 Opsonise Bacteria for Phagocytosis by Microglia

“…Calreticulin and galectin-3 are sugar-binding proteins known to have binding affinity for bacterial LPS (25, 26). LPS (lipopolysaccharide) contains many sugar residues and constitutes much of the surface of gram-negative bacteria.…”

“…Calreticulin can be found in the serum of healthy humans (at 5 ng/ml), and increases with inflammatory disease (35). Thus, serum calreticulin has the potential to opsonise bacteria in vivo , and the finding of calreticulin bound to LPS in the sera of patients with chronic bacterial infections suggests that is does (26).…”

Rab GTPase Mediating Regulation of NALP3 in Colorectal Cancer

“…NALP3 inflammasome activation requires two signals as follows: priming and activation [ 45 ]. LPS is commonly used as a priming signal [ 46 ], while the second signal could include multiple stimuli, including ATP and potassium efflux agents [ 47 ]. Nigericin, a microbial toxin, is a potassium ionophore and is often used as a second signal for NALP3 activation [ 48 , 49 ].…”

Calreticulin Blockade Attenuates Murine Acute Lung Injury by Inducing Polarization of M2 Subtype Macrophages

“…In addition to the phagocytotic effects of CALR in antitumor responses, CALR has also an important role in the pathogenesis of infectious and autoimmune diseases. CALR interacts with lipopolysaccharide (LPS), a component of the gram-negative bacterial cell wall via the N-and C-domain globular head region and the C-domain alone, participating in LPS-mediated anti-bacteria innate immunity (33,34). In addition, CALR participated in pathogenetic inflammation through activation of integrin alpha subunits (ITGAs) and subsequently increasing adhesion and infiltration of both T cells and neutrophils (11).…”