Kallistatin: a novel human tissue kallikrein inhibitor. Purification, characterization, and reactive center sequence.

A novel human tissue kallikrein inhibitor designated as kallistatin has been purified from plasma to apparent homogeneity by polyethylene glycol fractionation and successive chromatography on heparin-Agarose, DEAE-Sepharose, hydroxylapatite, and phenyl-Superose columns. A purification factor of 4350 was achieved with a yield of approximately 1.35 mg per liter of plasma. The purified inhibitor migrates as a single band with an apparent molecular mass of 58 kDa when analyzed on SDS-polyacrylamide gel electrophoresis under reducing conditions. It is an acidic protein with pI values ranging from 4.6 to 5.2. No immunological cross-reactivity was found by Western blot analyses between kallistatin and other serpins. Kallistatin inhibits human tissue kallikrein's activity toward kininogen and tripeptide substrates. The second-order reaction rate constant (ka) was determined to be 2.6 x 10(4) M-1 s-1 using Pro-Phe-Arg-MCA. The inhibition is accompanied by formation of an equimolar, heat- and SDS-stable complex between tissue kallikrein and kallistatin, and by generation of a small carboxyl-terminal fragment from the inhibitor due to cleavage at the reactive site by tissue kallikrein. Heparin blocks kallistatin's complex formation with tissue kallikrein and abolishes its inhibitory effect on tissue kallikrein's activity. The amino-terminal residue of kallistatin is blocked. Sequence analysis of the carboxyl-terminal fragment generated from kallistatin reveals the reactive center sequence from P1' to P15', which shares sequence similarity with, but is different from known serpins including protein C inhibitor, alpha 1-antitrypsin, and alpha 1-antichymotrypsin. The results show that kallistatin is a new member of the serpin superfamily that inhibits human tissue kallikrein.     

Human lysosomal protective protein. Glycosylation, intracellular transport, and association with beta-galactosidase in the endoplasmic reticulum.

In lysosomes beta-galactosidase and neuraminidase acquire a stable and active conformation through their association with the protective protein. The latter is homologous to serine carboxypeptidases and has cathepsin A-like activity which is distinct from its protective function towards the two glycosidases. To define signals in the human protective protein important for its intracellular transport, and to determine the site of its association with beta-galactosidase, we have generated a set of mutated protective protein cDNAs carrying targeted base substitutions. These mutants were either singly transfected into COS-1 cells or cotransfected together with wild type human beta-galactosidase. We show that all point mutations cause either a complete or partial retention of the protective protein precursor in the endoplasmic reticulum. This abnormal accumulation leads to degradation of the mutant proteins probably in this compartment. Only the oligosaccharide chain on the 32-kDa subunit acquires the mannose 6-phosphate recognition marker, the one on the 20-kDa subunit seems to be merely essential for the stability of the mature protein. In cotransfection experiments, wild type beta-galactosidase and protective protein appear to assemble already as precursors, soon after synthesis, in the endoplasmic reticulum. Mutated protective protein precursors that are retained in the endoplasmic reticulum or pre-Golgi complex interact with and withhold normal beta-galactosidase molecules in the same compartments, thereby preventing their normal routing.     

Regulation of Hsp70 function by a eukaryotic DnaJ homolog.

We report that a purified cytoplasmic Hsp70 homolog from Saccharomyces cerevisiae, Hsp70SSA1, exhibits a weak ATPase activity, which is stimulated by a purified eukaryotic dnaJp homolog (YDJ1p). Stable complex formation between Hsp70SSA1 and the permanently unfolded protein carboxymethylated alpha-lactalbumin (CMLA) was assayed by native gel electrophoresis. The affinity of Hsp70SSA1 for CMLA appeared to be regulated by YDJ1p. Significant reduction in both CMLA-Hsp70SSA1 complex formation and the release of CMLA pre-bound to Hsp70SSA1 was observed only in the presence of both YDJ1p and ATP. Thus, Hsp70SSA1 and YDJ1p interact functionally in the execution of Hsp70SSA1 chaperone activities in the eukaryotic cell.     

Relation between veratridine reaction dynamics and macroscopic Na current in single cardiac cells

Veratridine modification of Na current was examined in single dissociated ventricular myocytes from late-fetal rats. Extracellularly applied veratridine reduced peak Na current and induced a noninactivating current during the depolarizing pulse and an inward tail current that decayed exponentially (tau = 226 ms) after repolarization. The effect was quantitated as tail current amplitude, Itail (measured 10 ms after repolarization), relative to the maximum amplitude induced by a combination of 100 microM veratridine and 1 microM BDF 9145 (which removes inactivation) in the same cell. Saturation curves for Itail were predicted on the assumption of reversible veratridine binding to open Na channels during the pulse with reaction rate constants determined previously in the same type of cell at single Na channels comodified with BDF 9145. Experimental relationships between veratridine concentration and Itail confirmed those predicted by showing (a) half-maximum effect near 60 microM veratridine and no saturation up to 300 microM in cells with normally inactivating Na channels, and (b) half-maximum effect near 3.5 microM and saturation at 30 microM in cells treated with BDF 9145. Due to its known suppressive effect on single channel conductance, veratridine induced a progressive, but partial reduction of noninactivating Na current during the 50-ms depolarizations in the presence of BDF 9145, the kinetics of which were consistent with veratridine association kinetics in showing a decrease in time constant from 57 to 22 and 11 ms, when veratridine concentration was raised from 3 to 10 and 30 microM, respectively. As predicted for a dissociation process, the tail current time constant was insensitive to veratridine concentration in the range from 1 to 300 microM. In conclusion, we have shown that macroscopic Na current of a veratridine-treated cardiomyocyte can be quantitatively predicted on the assumption of a direct relationship between veratridine binding dynamics and Na current and as such can be successfully used to analyze molecular properties of the veratridine receptor site at the cardiac Na channel.     

In vivo metabolism of a mutant apolipoprotein, apoA-IIowa, associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis.

Apolipoprotein (apo) A-I is the major protein constituent of plasma high density lipoproteins (HDL). A kindred has been identified in which a glycine to arginine mutation at residue 26 in apoA-I is associated with hypoalphalipoproteinemia and hereditary systemic amyloidosis. We isolated the mutant protein, termed apoA-IIowa, from the plasma of an affected subject and studied its in vivo metabolism compared to that of normal apoA-I in two heterozygous apoA-IIowa subjects and two normal controls. Normal and mutant apoA-I were radioiodinated with 131I and 125I, respectively, reassociated with autologous plasma lipoproteins, and simultaneously injected into all subjects. Kinetic analysis of the plasma radioactivity curves demonstrated that the mutant apoA-IIowa was rapidly cleared from plasma (mean fractional catabolic rate [FCR] 0.559 day-1) compared with normal apoA-I (mean FCR 0.244 day-1) in all four subjects. The FCR of normal apoA-I was also substantially faster in the heterozygous apoA-IIowa subjects (mean FCR 0.281 days-1) than in the normal controls (mean FCR 0.203 days-1). Despite the rapid removal from plasma of apoA-IIowa, the cumulative urinary excretion of its associated radioactivity after 2 weeks (44%) of the injected dose) was substantially less than that associated with normal apoA-I (78% of injected dose), indicating extravascular sequestration of radiolabeled apoA-IIowa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Three-dimensional solution structure of apo-neocarzinostatin.

Two and three-dimensional solution nuclear magnetic resonance studies of the 11K apoprotein from natural antitumor agent neocarzinostatin (NCS) were extended to elucidation of the high-resolution structure by the use of restrained molecular dynamics computations. The refined structures attained convergency upon three steps of iterative calculations, in which more distance restraints were extracted from experimental data, and the existing distance bounds were optimized on the basis of computed structures. The solution structures of apo-NCS contain seven antiparallel beta-strands, which form two closely located beta-sheets and a short beta-segment. This protein lacks any alpha-helical component. The alignment of the seven beta-strands gives rise to a beta-barrel with an elongated diameter in one direction. The global structure of apo-NCS resembles that of the Ig-fold domain found in immunoglobulins and other structurally related beta-proteins. Residues responsible for side-chain packing and the possible salt-bridge formation important for protein folding were identified. Neocarzinostatin and the analogous proteins are known to exert their biological activity through the interaction of DNA with a chromophoric molecule, which is non-covalently bound to the apo-proteins. This molecular chromophore-binding site in apo-NCS is made of a cavity consisting of residues from the four-beta-stranded sheet and the short beta-segment. Although the solution structures of apo-NCS are similar to that of the analogous apoauromomycin in the crystalline state, difference in the shape of the binding cavities between the two was found. This study provides a structural basis for characterization of the specific recognition and molecular mechanism of the antitumor NCS chromophore binding to its host protein.     

The matrix protein of human immunodeficiency virus type 1 is required for incorporation of viral envelope protein into mature virions.

Accumulating evidence suggests that the matrix (MA) protein of retroviruses plays a key role in virus assembly by directing the intracellular transport and membrane association of the Gag polyprotein. In this report, we show that the MA protein of human immunodeficiency virus type 1 is also critical for the incorporation of viral Env proteins into mature virions. Several deletions introduced in the MA domain (p17) of human immunodeficiency virus type 1 Gag polyprotein did not greatly affect the synthesis and processing of the Gag polyprotein or the formation of virions. Analysis of the viral proteins revealed normal levels of Gag and Pol proteins in these mutant virions, but the Env proteins, gp120 and gp41, were hardly detectable in the mutant virions. Our data suggest that an interaction between the viral Env protein and the MA domain of the Gag polyprotein is required for the selective incorporation of Env proteins during virus assembly. Such an interaction appears to be very sensitive to conformational changes in the MA domain, as five small deletions in two separate regions of p17 equally inhibited viral Env protein incorporation. Mutant viruses were not infectious in T cells. When mutant and wild-type DNAs were cotransfected into T cells, the replication of wild-type virus was also hindered. These results suggest that the incorporation of viral Env protein is a critical step for replication of retroviruses and can be a target for the design of antiviral strategies.     

Mutational analysis of the promoter required for influenza virus virion RNA synthesis.

An in vitro RNA synthesis system was established in which the influenza virus virion (minus-sense) RNA was made from the synthetic plus-sense RNA (cRNA) template by the purified viral polymerase complex. The cRNA promoter was studied by mutational analysis using the in vitro system, and on the basis of these experiments, the first 11 nucleotides of the 3' noncoding sequence were found to contain the minimum promoter required for virion RNA synthesis. The addition of extra nucleotides at the 3' end decreased the promoter activity of the templates, indicating that the viral polymerase does not recognize an internal promoter efficiently. The wild-type and mutated RNA templates were also tested in vivo by using the ribonucleoprotein transfection system. In contrast to the in vitro system, it was found that the majority of mutations at the 3'-terminal sequence significantly decreased or abolished chloramphenicol acetyltransferase (CAT) expression. These results suggest that the cRNA promoter overlaps other essential cis elements required for chloramphenicol acetyltransferase expression in vivo.     

Pharmacological characterization of a novel muscarinic partial agonist, YM796, in transfected cells expressing the m1 or m2 muscarinic receptor gene.

To investigate the pharmacological effect of a novel compound YM796, we performed radioligand binding experiments and correlative biochemical experiments using the transfected murine fibroblast B82 cells which expressed the m1 and m2 muscarinic receptor genes (cloned cell lines designated as LK3-3 and M2LKB2-2, respectively). [3H](-)methyl-3-quinuclidinyl benzilate [( 3H](-)MQNB) binding in these transfected cell lines was inhibited by different optical isomers of YM796 and other muscarinic drugs, atropine, pirenzepine, AF-DX 116, as well as selected agonists. (-)YM796, (+)YM796 and (+/-)YM796 inhibited [3H](-)MQNB binding in LK3-3 cells with Ki values of 16.4 microM, 30.1 microM and 21.8 microM and in M2LKB2-2 cells with Ki values of 52.0 microM, 108 microM and 77.1 microM, respectively. From functional assays we found the two isomers, (-)YM796 and (+)YM796 had different intrinsic activities for the M1 and M2 muscarinic receptors. (-)YM796 revealed agonistic activity: stimulation of [3H]IP1 accumulation in LK3-3 cells with an EC50 value of 26.5 microM, which was less efficacious (the Emax value was 5.6 times basal) than carbachol, a full agonist (the Emax value was 17.2 times basal). Interestingly, (-)YM796 did not show significant inhibition of cAMP formation in M2LKB2-2 cells except at extremely high concentrations (greater than 1mM). (+)YM796 exhibited no significant efficacy for the M1 and M2 muscarinic receptors. These results suggest that (-)YM796 represents a muscarinic partial agonist with functional selectivity for the M1 muscarinic receptors whereas (+)YM796 shows no efficacy for either M1 or M2 muscarinic receptors in these transfected cells.     

Increase of plasma IL-6 concentration with age in healthy subjects.

The present study demonstrated that plasma IL-6 concentration was higher in older subjects than in younger ones and significantly in the male group (P = 0.02); Spearman rank correlation showed that plasma IL-6 concentration was positively correlated with age (r = 0.28, N = 55, P < 0.05); there was a highly significant correlation between the concentrations in plasma IL-6 and IL-1 alpha (r = 0.51, N = 52, P < 0.001). These findings suggest the possibility that age-related changes of plasma IL-6 and IL-1 alpha may provide a pathological basis for the susceptibility to such illness as commonly occurs in elderly people, especially Alzheimer's disease as the two interleukins can induce the production of alpha 1-antichymotrypsin and beta-amyloid protein precursor.