structural characterization of iron uptake from human transferrin

2010年主要完成了以下工作：

The following work was accomplished in 2010: Expression, Purification and Complexation of Bacterial and Human Proteins An expression system for TbpA has been developed and is capable of producing 0.2-0.4 mg/L of purified protein. A large scale preparation (27L) of E. coli transformed with a plasmid containing the gene for TbpA as well as an N-terminal His-Tag and a cleavage site are grown and induced with low level IPTG overnight and then harvested. We recently improved expression yields through targeted mutagenesis. We also introduced additional methionine residues for phasing of TbpA crystals. Purified TbpA forms crystals in 96 well plates which are being optimized. An expression system for TbpB has also been developed and is capable of producing 7-8 mg/L of purified protein. A medium scale preparation (4L) of E. coli transformed with a plasmid containing the gene for TbpB (a soluble construct lacking the N-terminal membrane anchor) as well as an N-terminal His-Tag and a cleavage site are grown and induced with high level IPTG for a few hours and then harvested. The cells are then lysed and membranes are separated via ultracentrifugation, and the soluble fraction is run over a Nickel-NTA column. The Nickel eluate is then further purified and can be bound to purified commercially available iron-bound human serum transferrin. Recently, we made the first in vitro complex of TbpA-TbpB bound to human transferrin (hTf) and this triple complex will be characterized by single particle electron microscopy. We also have crystallized TbpA in complex with hTf and have obtained a partial molecular replacement solution for the crystal structure using the coordinates of hTf which we solved in 2007. We recently obtained crystals of TbpA+hTf (180 kDa total) that diffract X-rays to 2.6 resolution. The structure was solved in August 2010 by molecular replacement using our hTf coordinates (Wally et al., JBC 2007) and various TonB-denepdent transporter models. This structure, the first of an outer membrane protein in complex with its full-length host target (exemplifying host pathogen interactions), should tell us much about the specificity for human transferrin, the residues involved in this interaction, where variable and conserved epitopes are located on the extracellular surface (useful for vaccine design), how iron is extracted from hTf, and how it is transported across the outer membrane. This structure is a landmark achievement, taking 12 years to complete, and its importance will be revealed in the coming months as we analyze the data and do some functional assays. We plan to submit a manuscript by the end of 2010.