Huntingtin interacting proteins are genetic modifiers of neurodegeneration.

Huntington's disease (HD) is a fatal neurodegenerative condition caused by expansion of the polyglutamine tract in the huntingtin (Htt) protein. Neuronal toxicity in HD is thought to be, at least in part, a consequence of protein interactions involving mutant Htt. We therefore hypothesized that genetic modifiers of HD neurodegeneration should be enriched among Htt protein interactors.

Strategic use of immunoprecipitation and LC/MS/MS for trace-level protein quantification: myosin light chain 1, a biomarker of cardiac necrosis.

Myosin light chain 1 (Myl3) is a 23-kDa isoform of one of the subunits of myosin, a protein involved in muscle contraction. Myl3 is presently being studied as a biomarker of cardiac necrosis to predict drug-induced cardiotoxicity, and in the work presented here, an LC/MS/MS assay was developed and validated to measure Myl3 in rat serum. The key steps in this approach involved immunoaffinity purification of Myl3 from serum followed by on-bead digestion with trypsin to release a surrogate peptide.

Ampicillin/penicillin-binding protein interactions as a model drug-target system to optimize affinity pull-down and mass spectrometric strategies for target and pathway identification.

The identification and validation of the targets of active compounds identified in cell-based assays is an important step in preclinical drug development. New analytical approaches that combine drug affinity pull-down assays with mass spectrometry (MS) could lead to the identification of new targets and druggable pathways. In this work, we investigate a drug-target system consisting of ampicillin- and penicillin-binding proteins (PBPs) to evaluate and compare different amino-reactive resins for the immobilization of the affinity compound and mass spectrometric methods to identify proteins from drug affinity pull-down assays.

Transducible heat shock protein 20 (HSP20) phosphopeptide alters cytoskeletal dynamics.

Activation of cyclic nucleotide dependent signaling pathways leads to relaxation of smooth muscle, alterations in the cytoskeleton of cultured cells, and increases in the phosphorylation of HSP20. To determine the effects of phosphorylated HSP20 on the actin cytoskeleton, phosphopeptide analogs of HSP20 were synthesized. These peptides contained 1) the amino acid sequence surrounding the phosphorylation site of HSP20, 2) a phosphoserine, and 3) a protein transduction domain.

Development of an LC-MALDI method for the analysis of protein complexes.

In this study, a two-dimensional LC-MALDI-TOF/TOF method has been developed for analyzing protein complexes. In our hands, the method has proven to be an excellent strategy for the analysis of protein complexes isolated in pull-down experiments. This is in part because the preservation of the chromatographic separation on a MALDI target yields an "unlimited" amount of time to obtain MS/MS spectra, making it possible to probe more deeply into complex samples.

Characterization of glycosylation sites of the epidermal growth factor receptor.

The epidermal growth factor receptor is a transmembrane glycoprotein that mediates the cellular responses to epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). In this study of the human EGF receptor naturally expressed in A431 cells, the glycosylation sites of the full-length, membrane-bound receptor and of a secreted form of the receptor were characterized by mass spectrometry. Our data show that the naturally expressed human EGF receptor is fully glycosylated on eight of the 11 canonical sites; two of the sites are not glycosylated, and one is partially glycosylated, a pattern of site-usage similar but not identical to those reported for the recombinant human EGF receptor heterologously expressed in Chinese hamster ovary cells.

Mutants of the CuA site in cytochrome c oxidase of Rhodobacter sphaeroides: II. Rapid kinetic analysis of electron transfer.

The function of the binuclear Cu(A) center in cytochrome c oxidase (CcO) was studied using two Rhodobacter sphaeroides CcO mutants involving direct ligands of the Cu(A) center, H260N and M263L. The rapid electron-transfer kinetics of the mutants were studied by flash photolysis of a cytochrome c derivative labeled with ruthenium trisbipyridine at lysine-55. The rate constant for intracomplex electron transfer from heme c to Cu(A) was decreased from 40000 s(-1) for wild-type CcO to 16000 s(-1) and 11000 s(-1) for the M263L and H260N mutants, respectively.

Mutants of the CuA site in cytochrome c oxidase of Rhodobacter sphaeroides: I. Spectral and functional properties.

To study the functional significance of the unusual bimetallic Cu(A) center of cytochrome c oxidase, the direct ligands of the Cu(A) center in subunit II of the holoenzyme were mutated. Two of the mutant forms, M263L and H260N, exhibit major changes in activity (10% and 1% of wild-type, respectively) and in near-infrared and EPR spectra, but metal analysis shows that both mutants retain two coppers in the Cu(A) center and both retain proton pumping activity. In M263L, multifrequency EPR studies indicate the coppers are still electronically coupled, while all the other metal centers in M263L appear unchanged, by visible, EPR, and FTIR spectroscopy.