Preference of calcium-dependent interactions between calmodulin-like domains of calpain and calpastatin subdomains

Purification of active calpain by affinity chromatography on an immobilized peptide inhibitor

Most purification schemes of calpain (CANP) involve a number of chromatographic steps. The final preparations often contain impurities, including degradation fragments. Two peptide-affinity columns were developed, using peptides of 27 amino acids and 30 amino acids, corresponding to the products of exons 1B and 1C, respectively, of the natural inhibitor (calpastatin) gene, coupled to CNBr-activated Sepharose 4B. Crude preparations of calpain, isolated by anion-exchange chromatography on a DEAE-Sepharose column, were incubated with a reversible or an irreversible synthetic inhibitor which blocks the catalytic subunit of the enzyme in the inactive 80-kDa form. The crude preparation was then loaded onto the peptide column in the presence of calcium. Calpain was eluted with an EGTA-containing buffer. Using the two peptide-affinity columns connected in tandem, calpain was isolated with a high degree of purity, suitable for structural and mechanistic studies, i.e. as an 80/30-kDa heterodimer or in the form of dissociated monomers.

Regulation of the calpain-calpastatin system by membranes (review)

Calpain, an intracellular calcium-dependent protease, is activated at cell membranes and cleaves cytoskeletal and submembranous proteins. Calpain is inferred to be a calcium-dependent regulator for cytoskeletal reorganization. Calpastatin, an endogenous calpain inhibitor, inhibits not only the proteolytic activity of calpain but also the binding of calpain to membranes. Calpain activity is strictly regulated by calcium and calpastatin. Calpain has two distinct sites for interaction with calpastatin, one the active site and the other an EF-hand domain. It is believed that calpain interacts with substrates through the same two sites. We discuss the regulation of membrane binding and the activity of calpain through these two sites.

An alpha-mercaptoacrylic acid derivative is a selective nonpeptide cell-permeable calpain inhibitor and is neuroprotective

Overactivation of calcium-activated neutral protease (calpain) has been implicated in the pathophysiology of several degenerative conditions, including stroke, myocardial ischemia, neuromuscular degeneration, and cataract formation. Alpha-mercaptoacrylate derivatives (exemplified by PD150606), with potent and selective inhibitory actions against calpain, have been identified. PD150606 exhibits the following characteristics: (i) Ki values for mu- and m-calpains of 0.21 microM and 0.37 microM, respectively, (ii) high specificity for calpains relative to other proteases, (iii) uncompetitive inhibition with respect to substrate, and (iv) it does not shield calpain against inactivation by the active-site inhibitor trans-(epoxysuccinyl)-L-leucyl-amido-3-methylbutane, suggesting a nonactive site action for PD150606. The recombinant calcium-binding domain from each of the large or small subunits of mu-calpain was found to interact with PD150606. In low micromolar range, PD15O6O6 inhibited calpain activity in two intact cell systems. The neuroprotective effects of this class of compound were also demonstrated by the ability of PD150606 to attenuate hypoxic/hypoglycemic injury to cerebrocortical neurons in culture and excitotoxic injury to Purkinje cells in cerebellar slices.

Kinetics of ligand binding to receptor immobilized in a polymer matrix, as detected with an evanescent wave biosensor. I. A computer simulation of the influence of mass transport

The influence of mass transport on ligand binding to receptor immobilized in a polymer matrix, as detected with an evanescent wave biosensor, was investigated. A one-dimensional computer model for the mass transport of ligand between the bulk solution and the polymer gel and within the gel was employed, and the influence of the diffusion coefficient, the partition coefficient, the thickness of the matrix, and the distribution of immobilized receptor were studied for a variety of conditions. Under conditions that may apply to many published experimental studies, diffusion within the matrix was found to decrease the overall ligand transport significantly. For relatively slow reactions, small spatial gradients of free and bound ligand in the gel are found, whereas for relatively rapid reactions strong inhomogeneities of ligand within the gel occur before establishment of equilibrium. Several types of deviations from ideal pseudo-first-order binding progress curves are described that resemble those of published experimental data. Extremely transport limited reactions can in some cases be fitted with apparently ideal binding progress curves, although with apparent reaction rates that are much lower than the true reaction rates. Nevertheless, the ratio of the apparent rate constants can be semiquantitatively consistent with the true equilibrium constant. Apparently "cooperative" binding can result from high chemical on rates at high receptor saturation. Dissociation in the presence of transport limitation was found to be well described empirically by a single or a double exponential, with both apparent rate constants considerably lower than the intrinsic chemical rate constant. Transport limitations in the gel can introduce many generally unknown factors into the binding progress curve. The simulations suggest that unexpected deviations from ideal binding progress curves may be due to highly transport influenced binding kinetics. The use of a thinner polymer matrix could significantly increase the range of detectable rate constants.