Biomedica biochimica acta最新文献

Two zymogens of matrix metalloproteinases (MMPs), proMMP-1 (tissue procollagenase) and proMMP-3 (prostromelysin) were isolated from the culture medium of human rheumatoid synovial fibroplasts and their activation mechanisms by proteinases and 4-aminophenylmercuric acetate (APMA) were studied by kinetic and sequence analyses. Both zymogens were activated by unique stepwise activation mechanisms through which sequential processing events occur in the propeptide regions. The initial cleavage sites attacked by activator proteinases are located in the middle of the propeptides at Glu33-Lys-Arg-Arg-Asn37 in proMMP-1 and Phe34-Val-Arg-Arg-Lys-Asp39 in proMMP-3. The initial products of proMMP-1 generated by proteinases then undergo further autocleavage of the Thr64-Leu65 bond. The treatment of proMMP-1 and proMMP-3 with APMA results in the intramolecular cleavage of the Val67-Met68 and Glu68-Val69 bonds, respectively. The removal of a portion of propeptides results in conformational changes around the Gln80-Phe81 and His82-Phe83 bonds in respective intermediates of MMP-1 and MMP-3 and render them to rapid specific cleavage by MMP-3 to generate stable, fully active enzymes.

Human polymorphonuclear leukocytes mainly protect the body against invading microorganisms. Therefore, cells must migrate to the site of infection, whereby they traverse the endothelial cell layer of the blood vessels, basement membranes and the connective tissue. We investigated the unknown mechanism of penetration of basement membranes by scanning electron microscopy. Our findings indicate a three-step mechanism--adhesion, locally limited proteolytic degradation of matrix components and mechanical loosening of the matrix. Finally, cells locomote in the stroma tissue to the site of infection. These processes are induced by formyl-peptides amongst others. In addition, an increased release of collagenase induced by formyl-peptides was observed. In contrast, incubation with prostaglandin F2 alpha led to significantly higher levels of secreted collagenase, while elastase failed to be detected in the supernatant of stimulated cells. Since it has been shown that collagenase is secreted in a latent form, we have focussed our attention on the activation mechanism of the proenzyme, which was investigated by determination of the N-terminal sequences of intermediate and final, activated forms.

The transglycosylation from raffinose and lactose to Aloc-Ser-OMe is catalyzed respectively by alpha and beta galactosidases. Transglycosylation from cellobiose has been achieved with beta-glucosidase. The simplicity of the enzymatic synthesis, the stereospecificity of the condensations in one-pot reactions and the ease of purification give the method value for large scale preparation of beta-linked derivatives. The protective groups of the serine residue can be cleaved under mild conditions: the ester group has been removed quantitatively by papain catalyzed hydrolysis and the Aloc group by a Pd (0) hydrostannolytic cleavage.

A novel membrane-bound serine esterase, named tryptase TL2, which is immunologically reactive with the antibody inhibiting induction of syncytia by human immunodeficiency virus-1 (HIV-1) (HATTORI, T., KOITO, A., TAKATSUKI, K., KIDO, H., and KATUNUMA, N., 1989, FEBS Lett., 248, 48-52), has been purified from a human T4+ lymphocyte clone. The enzyme has a molecular mass of 198 +/- 15 kDa, and is composed of two subunits of 32 kDa and four subunits of 28 kDa. The enzyme was strongly inhibited by the envelope glycoprotein gp120 of HIV-1, by synthetic peptides of V3 domains of gp120 s with the sequence GPGR in their center, which correspond to the principal neutralizing epitopes of the gp120s of various HIV-1 strains, by Kunitz-type inhibitors with the sequence GPCR in their active site, such as trypstatin, H130, and [Arg15, Glu52] aprotinin and by the microbial inhibitors leupeptin and antipain. This enzyme was specifically bound to the inhibitor V3 domain of gp120 of HIV-1, and this binding was blocked by the inhibitors of tryptase TL2, with a central motif GPCR or GPGR sequence in their center, but not by leupeptin and antipain without the motif. These findings suggest that tryptase TL2 is important in target site recognition and binding of HIV-1 in co-operation with CD4 receptor in the initial process of HIV-1 infection.

A two-step immunoaffinity isolation procedure for human alpha-fetoprotein (AFP) was developed resulting in highly purified AFP at high yield. A monoclonal antibody immunoadsorbent was used in the first step. Elution of AFP was carried out at alkaline pH by a solution of 0.5 mol/l ammonia containing 0.5 mol/l sodium chloride. To remove impurities caused by the first step, an anti-mouse immunoglobulin antibody immunoadsorbent was applied in the second step.

The growth-related protein p23 of the Ehrlich ascites tumor (EAT) is preferentially expressed in the exponentially growing tumor; its synthesis is translationally controlled. p23 mRNA is efficiently translated in the wheat germ cell-free lysate. In contrast, p23 mRNA present in poly(A)+RNA isolated from EAT is not translated in cell-free systems of EAT and reticulocytes. Moreover, translation of a p23 transcript is inhibited in the presence of total poly(A)+RNA. This inhibition is abolished by the removal of the 5'-UTR of the p23 transcript. Solution hybridization/RNase protection experiments point to the presence of a nucleotide sequence complementary to the 5'-UTR of p23 mRNA which might be involved in p23 mRNA inhibition.

ts85, a cell-line that harbors a mutant thermolabile ubiquitin-activating enzyme, E1, fails to degrade short-lived proteins at the restrictive temperature (Ciechanover, A., Finley, D., and Varshavsky, A. (1984) Cell 37, 57-66). It is not known whether the ubiquitin system is also involved in the degradation of long-lived proteins. In the present study we show that upon shifting the mutant cells to the restrictive temperature, there is no change in the rate of degradation of long-lived proteins. In contrast, shifting the wild-type cells (FM3A) to the high temperature is accompanied by a 2-fold increase in the rate of proteolysis of this group of proteins. This heat-induced accelerated degradation can be completely inhibited by NH4Cl and chloroquine. Similarly, exposure of the cells to starvation, a stimulus that activates the autophagic-lysosomal pathway, has no effect on the degradation of long-lived proteins in the mutant cells following inactivation of E1. Under the same conditions, the degradation rate in the wild-type cells increases almost 4-fold. A revertant of the ts85 cells behaved in a similar manner to the wild-type cells. Analogous results were obtained using a different cell line that also harbors a thermolabile E1 (ts20) (Kulka, R. G. et al. (1988) J. Biol. Chem. 263, 15726-15731). Cycloheximide and 3-methyladenine, inhibitors of formation of autophagic vacuoles, suppress the heat-induced accelerated degradation in the wild-type cells. Taken together, the results suggest that: 1. heat stress induces enhanced degradation of intracellular proteins, 2. the process occurs most probably in autophagic vacuoles, 3. activation of ubiquitin is required for enhanced degradation to occur, and 4. the activation is involved most probably in formation of the autophagic vacuoles.