Characterization of the affinity of streptavidin toward a peptide sequence previously identified as a target substrate for biotinylation by the escherichia coli biotin holoenzyme synthetase, BirA

Escherichia coli do not express Fc-receptors for human immunoglobulin G (IgG)

Gram-positive bacterial pathogens express immunoglobulin (Ig) binding proteins that perturb Fc-dependent functions such as the interaction with complement or phagocytic Fc-receptors. The possession of such molecules by gram-negative bacteria, including Escherichia coli (E. coli), has also been documented. In many such studies, the detection of Ig binding has relied on the use of polyclonal antibodies as detecting reagents. These are not ideal since such preparations may be contaminated with E. coli specific IgG, allowing for the potential misinterpretation of specific F(ab')(2) binding as non-specific Fc mediated binding. Here we use mono-specific recombinant antibodies to develop a novel assay for Ig binding non reliant on traditional polyclonal antibodies, allowing us to demonstrate the unequivocal absence of Fc binding proteins from E. coli.

The N-terminal fragment of GRP94 is sufficient for peptide presentation via professional antigen-presenting cells

The chaperone glucose-regulated protein 94 (GRP94) has long been used to augment peptide presentation to T cells. This chaperone binds antigenic peptides, binds to receptors on professional antigen-presenting cells (APCs), activates these cells and after internalization, transfers the peptides to MHC class I for activation of T cells. Here we show that all these activities reside within amino acids 1-355 of GRP94. This small fragment is sufficient to bind peptides, to bind and be taken up by the receptors CD91 and scavenger receptor type A on either dendritic cells or macrophages. The minimal construct can augment peptide presentation in culture and induce antigen-specific CTL in naive mice only because it loads APCs with the relevant peptide. Thus, the sequence 1-355 is the immunologically sufficient module of GRP94 and we propose that this 'mini-chaperone' can be used in immunotherapy of tumors and vaccine development.