False Positives in Brucellosis Serology: Wrong Bait and Wrong Pond?

This review summarizes the status of resolving the problem of false positive serologic results (FPSR) in Brucella serology, compiles our knowledge on the molecular background of the problem, and highlights some prospects for its resolution. The molecular basis of the FPSRs is reviewed through analyzing the components of the cell wall of Gram-negative bacteria, especially the surface lipopolysaccharide (LPS) with details related to brucellae. After evaluating the efforts that have been made to solve target specificity problems of serologic tests, the following conclusions can be drawn: (i) resolving the FPSR problem requires a deeper understanding than we currently possess, both of Brucella immunology and of the current serology tests; (ii) the practical solutions will be as expensive as the related research; and (iii) the root cause of FPSRs is the application of the same type of antigen (S-type LPS) in the currently approved tests. Thus, new approaches are necessary to resolve the problems stemming from FPSR. Such approaches suggested by this paper are: (i) the application of antigens from R-type bacteria; or (ii) the further development of specific brucellin-based skin tests; or (iii) the application of microbial cell-free DNA as analyte, whose approach is detailed in this paper.

Generation and characterization of D-dimer specific monoclonal antibodies for use in latex agglutination test.

The commercially available D-dimer assays used in the clinical practice often show differences in the results, and their specificity and sensitivity are rather unsatisfactory. Our aim was to develop a new monoclonal antibody against D-dimer with a proper specificity, and estimating its suitability using in a latex agglutination diagnostic test. Monoclonal antibodies were generated using hybridoma technology. Their titer was determined by a self-developed ELISA method. The cross-reactions of the antibodies were tested. Characterization of the epitope specificity of a selected antibody was performed through digestion of D-dimer followed by Western blotting. The amino acid sequences of the active antigen fragments were determined. According to the ELISA results, 38 cell groups were constated as antibody-producing hybridomas, among them 7 gave raised titer of antibody and were cloned. Based on the cross-reaction analysis, none of the antibodies gave cross-reaction with fibrin-E and fibrinogen-E fragments but reacted with fibrin D and fibrinogen D fragments. A low cross-reaction was showed with fibrinogen and fibrin X and Y. Contrary to the others, antibody 2B9 gave no cross-reaction with fibrinogen and reacted weakly with fibrin X and Y fragments. According to the epitope analysis the antibody 2B9 binds to amino acids 94-99 and to amino acids 140-147 on the beta chain and it recognizes the amino acids 23-32 and 93-98 on the gamma chain of D-dimer. Considering the characteristics of the above mentioned monoclonal antibody 2B9, we found that it is suitable to be a basis for a D-dimer diagnostic test with proper specificity.

Shotgun electroelution: a proteomic tool for simultaneous sample elution from whole SDS-polyacrylamide gel slabs.

A high-throughput device has been constructed which allows parallel electroelution of separated SDS-protein bands directly from intact unsectioned polyacrylamide gel slabs as well as single electroelution of certain protein spots into a 384-well standard flat-bottom multiwell plate. The prototype provides complete, quick elution for proteomics from 1-D or from 2-D gels without gel sectioning. Since the elution chamber matrix requires no assembly, sample handling can be easily carried out by existing robotic workstations. The current design is a good candidate for automation of spot elution since there are no moving liquid containing components in the apparatus. Eight SDS-proteins were eluted in test runs and an average 70% sample recovery was achieved by re-electrophoresis of the electro-eluates.

Myelin basic protein, an autoantigen in multiple sclerosis, is selectively processed by human trypsin 4.

Demyelination, the proteolytic degradation of the major membrane protein in central nervous system, myelin, is involved in many neurodegenerative diseases. In the present in vitro study the proteolytic actions of calpain, human trypsin 1 and human trypsin 4 were compared on lipid bound and free human myelin basic proteins as substrates. The fragments formed were identified by using N-terminal amino acid sequencing and mass spectrometry. The analysis of the degradation products showed that of these three proteases human trypsin 4 cleaved myelin basic protein most specifically. It selectively cleaves the Arg79-Thr80 and Arg97-Thr98 peptide bonds in the lipid bound form of human myelin basic protein. Based on this information we synthesized peptide IVTPRTPPPSQ that corresponds to sequence region 93-103 of myelin basic protein and contains one of its two trypsin 4 cleavage sites, Arg97-Thr98. Studies on the hydrolysis of this synthetic peptide by trypsin 4 have confirmed that the Arg97-Thr98 peptide bond is highly susceptible to trypsin 4. What may lend biological interest to this finding is that the major autoantibodies found in patients with multiple sclerosis recognize sequence 85-96 of the protein. Our results suggest that human trypsin 4 may be one of the candidate proteases involved in the pathomechanism of multiple sclerosis.

Extended intermolecular interactions in a serine protease-canonical inhibitor complex account for strong and highly specific inhibition.

We have previously shown that a trypsin inhibitor from desert locust Schistocerca gregaria (SGTI) is a taxon-specific inhibitor that inhibits arthropod trypsins, such as crayfish trypsin, five orders of magnitude more effectively than mammalian trypsins. Thermal denaturation experiments, presented here, confirm the inhibition kinetics studies; upon addition of SGTI the melting temperatures of crayfish and bovine trypsins increased 27 degrees C and 4.5 degrees C, respectively. To explore the structural features responsible for this taxon specificity we crystallized natural crayfish trypsin in complex with chemically synthesized SGTI. This is the first X-ray structure of an arthropod trypsin and also the highest resolution (1.2A) structure of a trypsin-protein inhibitor complex reported so far. Structural data show that in addition to the primary binding loop, residues P3-P3' of SGTI, the interactions between SGTI and the crayfish enzyme are also extended over the P12-P4 and P4'-P5' regions. This is partly due to a structural change of region P10-P4 in the SGTI structure induced by binding of the inhibitor to crayfish trypsin. The comparison of SGTI-crayfish trypsin and SGTI-bovine trypsin complexes by structure-based calculations revealed a significant interaction energy surplus for the SGTI-crayfish trypsin complex distributed over the entire binding region. The new regions that account for stronger and more specific binding of SGTI to crayfish than to bovine trypsin offer new inhibitor sites to engineer in order to develop efficient and specific protease inhibitors for practical use.

An electroelution apparatus for sequential transfer of sodium dodecyl sulfate-proteins into agarose and mass spectrometric identification of Li-Na-dodecyl sulfate-proteins from solubilized agarose.

Separated protein bands are sequentially electrophoresed into low melting agarose plugs distributed in an apparatus of original design along the surface of a plastic drum. The rotation of the drum is synchronized to migration of electrophoretic bands to receive each band individually. Agarose plugs are dissolved enzymatically for transfer into the mass spectrometer. One microL of the agarose solution containing 1 pmol of each of three lithium and natrium salts of dodecyl sulfate (Li-Na-DS)-proteins were applied to matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) without any prepurification. It yields a signal indistinguishable from that obtained in the absence of agarose.

Ala226 to Gly and Ser189 to Asp mutations convert rat chymotrypsin B to a trypsin-like protease.

In a previous successful attempt to convert trypsin to a chymotrypsin-like protease, 15 residues of trypsin were replaced with the corresponding ones in chymotrypsin. This suggests a complex mechanism of substrate recognition instead of a relatively simple one that only involves three sites, residues 189, 216 and 226. However, both trypsin-->elastase and chymotrypsin-->trypsin conversion experiments carried out according to the complex model resulted in non-specific proteases with low catalytic activity. Chymotrypsin used in the latter studies was of B-type, containing an Ala residue at position 226. Trypsins, however, contain a conserved Gly at this site. The substantially decreased trypsin-like activity of the G226A trypsin mutant also suggests a specific role for this site in substrate binding. Here we investigate the role of site 226 by introducing the A226G substitution into chymotrypsin-->trypsin mutants which were constructed according to both the simple (S189D mutant) and the complex model (S(1) mutant) of specificity determination. The kinetic parameters show that the A226G substitution in the S(1) mutant increased the chymotrypsin-like activity, while the trypsin-like activity did not change. In contrast, this substitution in the S189D chymotrypsin mutant resulted in a 100-fold increase in trypsin-like activity and a trypsin-like specificity profile as tested on a competing oligopeptide substrate library. Additionally, the S189D+A226G mutant is the first trypsin-like chymotrypsin that undergoes autoactivation, an exclusive property of trypsinogen among pancreatic serine proteases.

Mutant rat trypsin selectively cleaves tyrosyl peptide bonds.

A double mutant of rat trypsinogen (Asp189Ser, DeltaAsp223) was constructed by site-directed mutagenesis. The recombinant protein was produced in Escherichia coli under the control of a periplasmic expression vector. The purified and enterokinase-activated enzyme was characterized by synthetic fluorogenic tetrapeptide and natural polypeptide substrates and by a recently developed method. In case of this latter method the specificity profile of the enzyme was examined by simultaneous digestion of a mixture of oligopeptide substrates each differing only at the P(1) site residue, and the results were analyzed by high-performance liquid chromatography. All these assays unanimously demonstrated that the recombinant proteinase lacks trypsin-like activity but acquired a rather unique selectivity: it preferentially hydrolyses peptide bonds C-terminal to tyrosyl residues. This narrow specificity should be useful in peptide-analytical applications such as sequence-specific fragmentation of large proteins prior to sequencing.

Natural substrates and inhibitors of mannan-binding lectin-associated serine protease-1 and -2: a study on recombinant catalytic fragments.

Mannan-binding lectin-associated serine protease (SP) (MASP)-1 and MASP-2 are modular SP and form complexes with mannan-binding lectin, the recognition molecule of the lectin pathway of the complement system. To characterize the enzymatic properties of these proteases we expressed their catalytic region, the C-terminal three domains, in Escherichia coli. Both enzymes autoactivated and cleaved synthetic oligopeptide substrates. In a competing oligopeptide substrate library assay, MASP-1 showed extreme Arg selectivity, whereas MASP-2 exhibited a less restricted, trypsin-like specificity. The enzymatic assays with complement components showed that cleavage of intact C3 by MASP-1 and MASP-2 was detectable, but was only approximately 0.1% of the previously reported efficiency of C3bBb, the alternative pathway C3-convertase. Both enzymes cleaved C3i 10- to 20-fold faster, but still at only approximately 1% of the efficiency of MASP-2 cleavage of C2. We believe that C3 is not the natural substrate of either enzyme. MASP-2 cleaved C2 and C4 at high rates. To determine the role of the individual domains in the catalytic region of MASP-2, the second complement control protein module together with the SP module and the SP module were also expressed and characterized. We demonstrated that the SP domain alone can autoactivate and cleave C2 as efficiently as the entire catalytic region, while the second complement control protein module is necessary for efficient C4 cleavage. This behavior strongly resembles C1s. Each MASP-1 and MASP-2 fragment reacted with C1-inhibitor, which completely blocked the enzymatic action of the enzymes. Nevertheless, relative rates of reaction with alpha-2-macroglobulin and C1-inhibitor suggest that alpha-2-macroglobulin may be a significant physiological inhibitor of MASP-1.