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Structural determination of biomolecular interfaces by nuclear magnetic resonance of proteins with reduced proton density.

ABSTRACT: Protein interactions are important for understanding many molecular mechanisms underlying cellular processes. So far, interfaces between interacting proteins have been characterized by NMR spectroscopy mostly by using chemical shift perturbations and cross-saturation via intermolecular cross-relaxation. Although powerful, these techniques cannot provide unambiguous estimates of intermolecular distances between interacting proteins. Here, we present an alternative approach, called REDSPRINT (REDduced/Standard PRoton density INTerface identification), to map protein interfaces with greater accuracy by using multiple NMR probes. Our approach is based on monitoring the cross-relaxation from a source protein (or from an arbitrary ligand that need not be a protein) with high proton density to a target protein (or other biomolecule) with low proton density by using isotope-filtered nuclear Overhauser spectroscopy (NOESY). This methodology uses different isotropic labeling for the source and target proteins to identify the source-target interface and also determine the proton density of the source protein at the interface for protein-protein or protein-ligand docking. Simulation indicates significant gains in sensitivity because of the resultant relaxation properties, and the utility of this technique, including a method for direct determination of the protein interface, is demonstrated for two different protein-protein complexes.

SUBMITTER: Ferrage F

PROVIDER: S-EPMC3637030 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Structural determination of biomolecular interfaces by nuclear magnetic resonance of proteins with reduced proton density.

Ferrage Fabien F Dutta Kaushik K Shekhtman Alexander A Cowburn David D

Journal of biomolecular NMR 20100407 1

Protein interactions are important for understanding many molecular mechanisms underlying cellular processes. So far, interfaces between interacting proteins have been characterized by NMR spectroscopy mostly by using chemical shift perturbations and cross-saturation via intermolecular cross-relaxation. Although powerful, these techniques cannot provide unambiguous estimates of intermolecular distances between interacting proteins. Here, we present an alternative approach, called REDSPRINT (REDd ...[more]

PMID: 20372977

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Project description:The serine proteases constitute a group of endopeptidases whose members owe their catalytic activity to the presence of a catalytic triad of amino acids consisting of a serine, a histidine and an aspartate. The pK(a) values for this histidine have been determined for several cases in which there is a negative charge installed at the serine to mimic the oxyanionic intermediate and related transition state for the catalytic pathway. Instances from this laboratory include (1) replacement of the serine by a cysteine in subtilisin to create a thiolate; (2) formation of monoisopropylphosphoryl-Ser 195 monoanionic phosphodiesters (in trypsin and chymotrypsin, Ser 221 in subtilisins); and (3) tetrahedral boronates formed with peptide boronic acids. The nuclear magnetic resonance (NMR) signals pertinent to this histidine, or signals indirectly reflecting the state of ionization of this histidine, have been used effectively to monitor changes in the active center ionization state. In every case studied, there is elevation of the pK(a) at the histidine when the negative charge is installed at the serine position. Herein is reported the first NMR measurement of the active center His 63 pK(a) in thiolsubtilisin Carlsberg; it is elevated by 3 units compared with the parent enzyme. Using a numerical solution (finite difference) of the Poisson-Boltzmann equation, a protein dielectric constant of 4 provides a good estimate of the experimentally observed pK(a) elevations. Very significantly, a very low protein dielectric constant (epsilon(p) = 3-5) is required in all of the comparisons, and for all three enzymes used (chymotrypsin, trypsin, and subtilisin). Finally, we discuss why the electrostatic perturbation sensed at His of the active center is more amplified by a negative charge on the Ser side than the same charge on the Asp side. A plausible explanation is that the positive charge on the imidazolium ring of the His is localized, with the N(delta 1) carrying a smaller fraction, the N(epsilon 2) carrying the bulk of the positive charge.

Dataset Information

Structural determination of biomolecular interfaces by nuclear magnetic resonance of proteins with reduced proton density.

Publications

Structural determination of biomolecular interfaces by nuclear magnetic resonance of proteins with reduced proton density.

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