Distinct CD4+ helper T cells involved in primary and secondary responses to infection.

Helper T cells are critical for protective immunity, CD8(+) T-cell memory, and CD4(+) recall responses, but whether the same or distinct CD4(+) T cells are involved in these responses has not been established. Here we describe two CD4(+) T cells, LLO118 and LLO56, specific for an immunodominant Listeria monocytogenes epitope, with dramatically different responses to primary and secondary infection. Comparing in vivo responses, LLO118 T cells proliferate more strongly to primary infection, whereas surprisingly, LLO56 has a superior CD4(+) recall response to secondary infection.

Dynamics and function in a bacterial ABC transporter: simulation studies of the BtuCDF system and its components.

ABC transporters are integral membrane proteins which couple the energy of ATP hydrolysis to the translocation of solutes across cell membranes. BtuCD is a approximately 1100-residue protein found in the inner membrane of Gram-negative bacteria which transports vitamin B12. Vitamin B12 is bound in the periplasm by BtuF, which delivers the solute to the periplasmic entrance of the transporter protein complex BtuCD.

3-D structural and functional characterization of the purified KATP channel complex Kir6.2-SUR1.

ATP-sensitive potassium (K(ATP)) channels conduct potassium ions across cell membranes and thereby couple cellular energy metabolism to membrane electrical activity. Here, we report the heterologous expression and purification of a functionally active K(ATP) channel complex composed of pore-forming Kir6.2 and regulatory SUR1 subunits, and determination of its structure at 18 A resolution by single-particle electron microscopy.

Nucleotide binding to the homodimeric MJ0796 protein: a computational study of a prokaryotic ABC transporter NBD dimer.

Transport by ABC proteins requires a cycle of ATP-driven conformational changes of the nucleotide binding domains (NBDs). We compare three molecular dynamics simulations of dimeric MJ0796: with ATP was present at both NBDs; with ATP at one NBD but ADP at the other; and without any bound ATP. In the simulation with ATP present at both NBDs, the dimeric protein interacts with the nucleotides in a symmetrical manner.

Identification of a functionally important negatively charged residue within the second catalytic site of the SUR1 nucleotide-binding domains.

The ATP-sensitive K+ channel (KATP channel) couples glucose metabolism to insulin secretion in pancreatic beta-cells. It is comprised of sulfonylurea receptor (SUR)-1 and Kir6.2 proteins.

Nucleotide-dependent conformational changes in HisP: molecular dynamics simulations of an ABC transporter nucleotide-binding domain.

ATP-binding cassette (ABC) transporters mediate the movement of molecules across cell membranes in both prokaryotes and eukaryotes. In ABC transporters, solute translocation occurs after ATP is either bound or hydrolyzed at the intracellular nucleotide-binding domains (NBDs). Molecular dynamics (MD) simulations have been employed to study the interactions of nucleotide with NBD.

Potassium channel regulation.

The sulphonylurea receptor (SUR) is a member of the ATP-binding cassette (ABC) family of membrane proteins. It functions as the regulatory subunit of the ATP-sensitive potassium (KATP) channel, which comprises SUR and Kir6.x proteins.

An atomic detail model for the human ATP binding cassette transporter P-glycoprotein derived from disulfide cross-linking and homology modeling.

The multidrug resistance P-glycoprotein mediates the extrusion of chemotherapeutic drugs from cancer cells. Characterization of the drug binding and ATPase activities of the protein have made it the paradigm ATP binding cassette (ABC) transporter. P-glycoprotein has been imaged at low resolution by electron cryo-microscopy and extensively analyzed by disulphide cross-linking, but a high resolution structure solved ab initio remains elusive.

Molecular modeling correctly predicts the functional importance of Phe594 in transmembrane helix 11 of the multidrug resistance protein, MRP1 (ABCC1).

The human ATP-binding cassette (ABC) transporter, multidrug resistance protein 1 (MRP1/ABCC1), confers resistance to a broad range of anti-cancer agents and transports a variety of organic anions. At present, essentially no structural data exists for MRP1 that might be used to elucidate its mechanism of transport. Consequently, we have applied a modeling strategy incorporating crystal and indirect structural data from other ABC transporters to construct a model of the transmembrane domains of the core region of MRP1 that includes the amino acid side chains.

Extending the structure of an ABC transporter to atomic resolution: modeling and simulation studies of MsbA.

Molecular modeling and simulation approaches have been use to generate a complete model of the prokaryotic ABC transporter MsbA from Escherichia coli, starting from the low-resolution structure-based Calpha trace (PDB code 1JSQ). MsbA is of some biomedical interest as it is homologous to mammalian transporters such as P-glycoprotein and TAP. The quality of the MsbA model is assessed using a combination of molecular dynamics simulations and static structural analysis.