The Exosporium of B.cereus Contains a Binding Site for gC1qR/p33: Implication in Spore Attachment and/or Entry

Abstract

B. cereus, is a member of a genus of aerobic, gram-positive, spore-forming rod-like bacilli, which includes the deadly, B. anthracis. Preliminary experiments have shown that gC1qR binds to B. cereus spores that have been attached to microtiter plates. The present studies were therefore undertaken, to examine if cell surface gC1qR plays a role in B. cereus spore attachment and/or entry. Monolayers of human colon carcinoma (Caco-2) and lung cells were grown to confluency on 6 mm coverslips in shell vials with gentle swirling in a shaker incubator. Then, 2 microl of a suspension of strain SB460 B. cereus spores (3x10(8)/ml, in sterile water), were added and incubated (1-4 h; 36 degrees C) in the presence or absence of anti-gC1qR mAb-carbon nanoloops. Examination of these cells by EM revealed that: (1) When B. cereus endospores contacted the apical Caco-2 cell surface, or lung cells, gC1qR was simultaneously detectable, indicating upregulation of the molecule. (2) In areas showing spore contact with the cell surface, gC1qR expression was often adjacent to the spores in association with microvilli (Caco-2 cells) or cytoskeletal projections (lung cells). (3) Furthermore, the exosporia of the activated and germinating spores were often decorated with mAb-nanoloops. These observations were further corroborated by experiments in which B.cereus spores were readily taken up by monocytes and neutrophils, and this uptake was partially inhibited by mAb 60.11, which recognizes the C1q binding site on gC1qR. Taken together, the data suggest a role, for gC1qR at least in the initial stages of spore attachment and/or entry.

The Exosporium Layer of Bacterial Spores: a Connection to the Environment and the Infected Host

“…Furthermore, C1q acted as a bridging molecule between BclA and integrin ␣ 2 ␤ 1 to mediate B. anthracis spore entry into epithelial cells in a complement activation-independent manner. A binding protein for the globular head domains of complement component C1q, designated gC1qR, was also reported to be involved in at least the initial stages of B. cereus spore attachment and/or entry (131).…”

Treatment with p33 Curtails Morbidity and Mortality in a Histone-Induced Murine Shock Model

“…In addition to these ligands, a number of bacterial and viral proteins have been identified that can bind either to surface-bound or intracellular p33 [28]. While the interactions of bacterial proteins with membrane-attached p33 is thought to promote cell adhesion and internalization of the pathogen [29,30,31], the interaction with viral proteins mainly takes place intracellularly and, in some cases, this has been shown to suppress virus replication [28]. Recently, we reported that p33 exhibits a high affinity for another group of proteins/peptides, namely AMPs.…”

Outer Structures of theBacillus anthracisSpore

“…Intriguingly, the C terminal domain of BclA (which is exposed at the spore surface) has high structural similarity to the portion of the complement protein C1q that binds antibody (Rety et al, 2005 ). Possible clues to the signifi cance of the structural similarity of BclA and C1q come from studies suggesting that B. cereus spores utilize the C1q receptor on lung and colon epithelial cells to facilitate attachment and entry of spores into the host (Ghebrehiwet et al, 2007 ). Perhaps, in the case of anthrax, interactions between BclA and C1q receptors on lung epithelial cells somehow facilitate phagocytosis by resident dendritic cells or alveolar macrophages.…”