Light scattering and pH titration were used to examine the binding of bovine serum albumin (BSA) to poly-(diallyldimethylammonium chloride) (PDADMAC), poly(acrylamidomethylpropyl sulfonate) (PAMPS), poly-(methacrylamidopropyltrimethylammonium chloride) (PMAPTAC), and an AMPS-acrylamide random copolymer (PAMPS 80 AAm 20 ). The critical protein charge required to induce protein-polyelectrolyte complexation, (Zpr) c , was found to vary linearly with the square root of the ionic strength (I 1/2 ), i.e., with the Debye-Hu ¨ckel parameter (κ), the proportionality constant being a function of polyelectrolyte chain parameters such as intrinsic stiffness and charge density. This linearity was remarkably continuous through Zpr ) 0, with (Zpr) c occurring predominantly "on the wrong side" of the isoionic point; i.e., the onset of binding was typically observed when the global protein charge was of the same sign as the polyelectrolyte. Binding of BSA to the lower charge density polyanion (PAMPS 80 AAm 20 ) unexpectedly occurred under conditions where binding to the more highly charged homopolyanion (PAMPS) did not. The theoretical treatment of Muthukumar was used to interpret the linearity of (Zpr) c vs I 1/2 and the observed influence of polyelectrolyte structural parameters. The apparent applicability of this model to the heterogeneous amphoteric protein surface suggests that binding of polyelectrolytes takes place at "charge patches" whose effective charge densities are different from, but nevertheless linearly dependent on, the global charge density.

The separation of proteins by polyelectrolyte coacervation or precipitation is based on electrostatically-driven complex formation. We have investigated complexation between the globular protein BSA and the polyelectrolyte poly(dimethyldially1ammonium chloride) (PDMDAAC) using light-scattering techniques to monitor solution turbidity. Turbidimetric pH titrations were used to determine the specific pH values where soluble complex formation is initiated (pH,) and where phase separation occurs (pH& These values, collected a t different ionic strengths, can be presented as phase boundaries. The effects of macromolecular concentration, protein:polymer concentration ratio (r), and polymer molecular weight upon the phase boundary are examined. The macromolecular concentration and polymer molecular weight have little or no effect on the phase boundary. While pH, is independent of r, pH$ varies inversely with r. The use of phase boundaries in the selection of optimal pH and ionic strength for maximum yield and purity in protein separations is discussed.

Objective. To identify, characterize, and compare proteolysis peptide products generated by metalloprotease digests of human articular cartilage.Methods. Human articular cartilage was digested by the addition of exogenous metalloproteases, including matrix metalloproteinases 2, 3, 8, 9, 12, and 13 and aggrecanases ADAMTS-4 and ADAMTS-5. Proteolyzed peptide products were identified by proteomics methods using mass spectrometry.Results. Complete sequences of the peptides proteolyzed from human articular cartilage, including Nand C-termini and hydroxylated posttranslational modifications, were determined. A wide variety of peptides, originating from types I, II, and III collagen, biglycan, prolargin, fibromodulin, fibronectin, decorin, cartilage oligomeric matrix protein, cartilage intermediate-layer protein, megakaryocyte-stimulating factor, mimecan, aggrecan, and lumican, was analyzed following metalloprotease digestion. Release of peptides varied as a function of time, enzyme specificity, and abundance. Specific type II collagen peptide biomarkers, including those containing the three-quarter-length fragment cleavage site and those containing the domains for helical peptide of type II collagen and C-telopeptide of type II collagen, were observed after release by selected proteases.Conclusion. The use of intact cartilage instead of purified protein substrates in the assay allowed for the identification of novel potential substrates and cleavage sites for individual enzymes under more physiologically relevant conditions. Characterization of these cartilage matrix peptides may help in the development of pharmacodynamic biomarkers of cartilage degradation, and also may contribute to an understanding of the bioactive peptides important in chondrocyte signaling.Osteoarthritis (OA) and rheumatoid arthritis (RA) are typified by biologic changes in the articular cartilage that lead to cartilage degradation and joint space narrowing (1,2). Articular cartilage is composed of 2 primary matrix proteins, type II collagen and aggrecan, as well as a number of other matrix proteins that provide structural functions such as rigidity, flexibility, and compression damping. In addition, the cartilage matrix influences chondrocyte function through integrin receptor signaling, initiated via ligation of either intact matrix molecules or peptide fragments resulting from proteolytic activity (3).In arthritis, an imbalance of chondrocyte matrix synthesis and degradation leads to a net loss of matrix, and eventually to joint impairment. In OA, the excessive degradation is primarily due to the action of proteases released by chondrocytes, synovial cells, and macrophages (4). Numerous serine proteases and metalloproteases are overexpressed by these cells during the disease process, but specific metalloproteases, including the collagenase matrix metalloproteinase 13 (MMP-13) and the aggrecanase ADAMTS-5, are thought to be especially important for initiating and promoting cartilage matrix degradation in OA (5,6). MMP-13 cleaves type II collage...

The recognition and cleavage of tRNAPhe and the TAR RNA of HIV-1 by metallopeptides of the general form Ni(II).Xaa-Gly-His (where Xaa is Gly, Lys, or Arg) were investigated. The results of RNA cleavage analyses suggest that KHSO5- or magnesium monoperoxyphthalate-activated metallopeptides (1) induce nucleobase damage which requires aniline acetate for complete RNA strand scission and (2) selectively target the loops of stem-loop structures of the above-named substrates. In targeting RNA loop regions, the metallopeptides may be sensitive to intraloop structural features, including the overall structural environment of the loop itself and possibly the presence of intraloop hydrogen bonding. Overall, these results suggest that the metallopeptides interact selectively within a loop, in a fashion reminiscent of many RNA binding proteins, instead of targeting RNA single-stranded character alone. These observations further suggest a possible metallopeptide-based strategy for the molecular recognition of native RNA structures and insight with regard to the general features available for ligand binding site discrimination.

We have developed a novel ELISA using an optimized ARGS antibody and have demonstrated for the first time, an ELISA-based measurement of aggrecan degradation products in human serum and urine. This assay has the potential to serve as a mechanistic drug activity biomarker in the clinic and is expected to significantly impact/accelerate the clinical development of aggrecanase inhibitors and other disease modifying drugs for OA.

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