Protein products of the rat kallikrein gene family. Substrate specificities of kallikrein rK2 (tonin) and kallikrein rK9.

Two closely related kallikrein-like proteinases having little activity toward the standard synthetic amide substrates of tissue kallikreins were isolated from the rat submandibular gland. They were found to be the protein products of the rKlk2 (tonin) and the rKlk9 genes by amino acid sequence analysis (nomenclature of the genes and proteins of the kallikrein family is according to the proposal of the discussion panel from the participants of the KININ '91 meeting held Sept. 8-14, 1991, in Munich, Germany). These two proteinases of similar structure also had very similar physicochemical properties. They differed from other kallikrein-related proteinases in having high pHi values of 6.20 (rK2) and 6.85 (rK9). Kallikrein rK2 was purified as a single peptide chain, whereas rK9 appeared as a two-chain protein after reduction. Their enzymatic properties were also very similar and differed significantly from those of other rat kallikrein-related proteinases. Unlike the five other kallikrein-related proteinases we have purified so far, kallikrein rK9 was not inhibited by aprotinin. rK9 also differed from rK2 by its tissue localization. The prostate gland contained only rK9 where it was the major kallikrein-like component. The amino acids preferentially accommodated by the proteinase S3 to S2' subsites were identified using synthetic amide and protein substrates. Unlike other kallikrein-related proteinases, rK2 had a prevalent chymotrypsin-like specificity, whereas rK9 had both chymotrypsin-like and trypsin-like properties. Both rK2 and rK9 preferred a prolyl residue in position P2 of the substrate and did not accommodate bulky and hydrophobic residues at that position, as did most of the other kallikrein-related proteinases. This P2-proline-directed specificity is necessary for processing the precursors of several biologically active peptides. Subsites accommodating residues COOH-terminal to the scissile bond were also important in determining the overall substrate specificity of these proteinases. rK2 and rK9 both showed a preference for hydrophobic residues in P2'. Other subsites upstream of the S3 subsite were found to intervene in substrate binding and hydrolysis. The restricted specificity of rK2 and rK9 is consistent with the presence of an extended substrate binding site, and hence with a processing enzyme function. Their P1 specificities enabled both proteinases to release angiotensin II from angiotensinogen and from angiotensinogen I, but rK9 was at least 100 times less active than rK2 on both substrates. The substrate specificities of rK2 and rK9 were correlated with key amino acids defining their substrate binding site.(ABSTRACT TRUNCATED AT 400 WORDS)     

Purification and characterization of active recombinant rat kallikrein rK9.

The rat tissue kallikrein rK9 is most abundant in the submandibular gland and the prostate. It has been successfully expressed in the Pichia pastoris yeast expression system. A full-length cDNA coding for the mature rK9 was fused in frame with yeast alpha-factor cDNA. The fusion protein was secreted into the medium with high yield without being processed by the yeast KEX2 signal peptidase. Mature rK9 was efficiently released from the fusion protein by trypsin and was purified to homogeneity by one-step affinity chromatography using soya bean trypsin inhibitor (SBTI) as affinity ligand. The identity of the recombinant enzyme was checked by N-terminal amino acid sequencing, Western blot analysis and kinetic studies. The dual trypsin- and chymotrypsin-like enzymatic specificity of rK9 was assessed by determining specificity constants (k(cat)/K(m)) for the hydrolysis of fluorogenic substrates, the peptide sequences of which were derived from proparathyroid hormone (pro-PTH) and from semenogelin-I. Our results confirmed the presence of an extended binding site in the rK9 active site. We also identified a far more sensitive substrate of this enzyme than those previously described, Abz-VKKRSARQ-EDDnp, which was hydrolysed with a catalytic efficiency k(cat)/K(m) of 420000 M(-1)s(-1). Finally, we showed that four of the five major proteins contained in secretions of rat seminal vesicles were rapidly degraded by recombinant rK9.     

Diagnostic value of rK39 dipstick in zoonotic visceral leishmaniasis in Turkey

K39 is a repetitive immunodominant epitope in a kinesin-related protein expressed predominantly in the amastigotes of visceral Leishmania spp. Enzyme immunoassays of patient's sera with recombinant K39 (rK39) proved to be highly specific and sensitive for diagnosis of active visceral leishmaniasis (VL, kala-azar). The same assays in dipstick format were also found effective for diagnosis of both human VL (HVL) and canine VL (CanVL) in most endemic areas of these diseases. Fifty-eight human patients and 22 dogs, clinically suspected of kala-azar, were screened with rK39 dipstick in comparison with the conventional methods of diagnosis, i.e., microscopic examinations of bone marrow and lymph node aspirates and immunofluorescent antibody tests (IFAT), respectively. Sixteen patients and 12 dogs were found to be rK39 dipstick positive. The results were corroborated with those of parasitological examinations, except 1, rK39-positive but smear-negative, case in each group. IFAT of the 2 discordant cases gave positive results. The rK39 dipstick is thus reliable for diagnosis of both HVL and canVL cases in Turkey.     

Development and evaluation of Leishmania infantum rK26 ELISA for serodiagnosis of visceral leishmaniasis in Iran

The purpose of this study was to prepare recombinant K26 antigen from Leishmania infantum and evaluate its performance by enzyme-linked immunosorbent assay (ELISA) test for serodiagnosis of visceral leishmaniasis (VL) in endemic regions of Iran. The results were compared with those obtained by direct agglutination test (DAT) and whole cell ELISA using crude parasite antigen. Of 93 sera from patients with confirmed VL, 90 sera were positive with rK26 ELISA (sensitivity=96.8%), whereas 85 sera were positive with DAT (sensitivity=91.4%) and 89 sera were positive with whole cell ELISA (sensitivity=95.7%). Of 130 subjects who either had other infectious diseases (n=30) or were healthy (n=100), rK26 ELISA were negative in all cases (specificity=100%), whereas DAT were negative in 116 cases (specificity=89.2%) and whole cell ELISA was negative in 114 cases (specificity=87.7%). The results of this study indicate that the rK26 ELISA is more sensitive and specific than conventional methods and could be used for reliable diagnosis of VL caused by Leishmania infantum.     

Design,Development and Evaluation of rK28-Based Point-of-Care Tests for Improving Rapid Diagnosis of Visceral Leishmaniasis

Background

Visceral leishmaniasis (VL) is diagnosed by microscopic confirmation of the parasite in bone marrow, spleen or lymph node aspirates. These procedures are unsuitable for rapid diagnosis of VL in field settings. The development of rK39-based rapid diagnostic tests (RDT) revolutionized diagnosis of VL by offering high sensitivity and specificity in detecting disease in the Indian subcontinent; however, these tests have been less reliable in the African subcontinent (sensitivity range of 75–85%, specificity of 70–92%). We have addressed limitations of the rK39 with a new synthetic polyprotein, rK28, followed by development and evaluation of two new rK28-based RDT prototype platforms.

Methodology/Principal Findings

Evaluation of 62 VL-confirmed sera from Sudan provided sensitivities of 96.8% and 93.6% (95% CI = K28: 88.83–99.61%; K39: 84.30–98.21%) and specificities of 96.2% and 92.4% (95% CI = K28: 90.53–98.95%; K39: 85.54–96.65%) for rK28 and rK39, respectively. Of greater interest was the observation that individual VL sera with low rK39 reactivity often had much higher rK28 reactivity. This characteristic of the fusion protein was exploited in the development of rK28 rapid tests, which may prove to be crucial in detecting VL among patients with low rK39 antibody levels. Evaluation of two prototype lateral flow-based rK28 rapid tests on 53 VL patients in Sudan and 73 VL patients in Bangladesh provided promisingly high sensitivities (95.9% [95% CI = 88.46–99.1 in Sudan and 98.1% [95% CI = 89.93–99.95%] in Bangladesh) compared to the rK39 RDT (sensitivities of 86.3% [95% CI = 76.25–93.23%] in Sudan and 88.7% [95% CI = 76.97–95.73%] in Bangladesh).

Conclusions/Significance

Our study compares the diagnostic accuracy of rK39 and rK28 in detecting active VL cases and our findings indicate that rK28 polyprotein has great potential as a serodiagnostic tool. A new rK28-based RDT will prove to be a valuable asset in simplifying VL disease confirmation at the point-of-care.     

Evaluation of the direct agglutination test and the rK39 dipstick test for the sero-diagnosis of visceral leishmaniasis

The direct agglutination test (DAT) based on a freeze-dried antigen and the rK39 dipstick test were evaluated for the sero-diagnosis of visceral leishmaniasis (VL). The sensitivity and specificity of both tests were determined using sera from confirmed VL patients (n = 21), healthy controls (n = 19) and from patients with other confirmed infectious diseases (n = 42). The DAT had a sensitivity and a specificity of 100%. The rK39 had a sensitivity of 85.7% and a specificity of 82%. Both tests were also used to screen blood samples of confirmed VL patients (n = 15) and serum samples of VL suspects (n = 61). The DAT found all blood samples of confirmed VL patients positive and tested 98.4% of the serum samples of the VL suspects positive. In contrast, rK39 detected in 9/15 blood samples (60%) antibodies against Leishmania chagasi and found 85.3% of the serum samples of the suspected patients positive. Although the rK39 dipstick is more rapid and user friendlier than the DAT, the latter has a superior sensitivity and specificity. Furthermore, the reagents used for DAT do not require cold storage, whereas the buffer of the rK39 must be stored at 4oC. Therefore, the DAT is the most suitable test for the sero-diagnosis of VL under field conditions.     

Expression of Bacillus pumilus keratinase rK27 in Bacillus subtilis: enzyme application for developing renewable flocculants from bone meal

In this study thermostable keratinase rK₂₇ of Bacillus pumilus KS12 was expressed and secreted in Bacillus subtilis WB980 expression system under the control of xylose promoter (PxylA). The concentration of the recombinant keratinase rK₂₇ produced by B. subtilis reached 4,432 U/mL after 24 h of culture at 37 °C and 200 rpm with 0.5 % xylose at an initial concentration of 0.3 OD_600nm. Using the one-factor-at-a-time approach, we achieved an improvement in enzyme yield of up to 3.4-fold (15,390 U/mL) in the presence of 3 % yeast extract and 0.5 % tryptone. The enzyme was purified to homogenity using nickel affinity chromatography with a 3.63-fold purity and 80 % recovery. The purified enzyme rK₂₇ hydrolyzed 1 g bone meal after 12 h at 40 °C, pH 9, with a maximum protein release of 37.3 mg/g bone meal; in comparison subtilisin Carlsberg hydrolyzed 19.3 mg/g bone meal and proteinase K hydrolyzed 6.2 mg/g bone meal. The hydrolysate obtained after hydrolysis of bone by rK₂₇ was found to be effective as a flocculant at 0.1 mg in a 10 % (w/v) kaolin solution when compared with hydrolysates obtained from substilisin Carlsberg and proteinase K, which were effective at 0.5 mg and >2 mg, respectively.     

Specificity of the rapid rK39 antigen-based immunochromatographic test Kalazar Detect(r) in patients with cutaneous leishmaniasis in Brazil

The aim of this study was to evaluate the specificity of a rapid immunochromatographic test that was developed to detect antibodies against the rK39 antigen for the diagnosis of visceral leishmaniasis (VL). This evaluation was performed using sera from patients with a confirmed diagnosis of active cutaneous leishmaniasis. The sera from 272 patients with a confirmed diagnosis of localised cutaneous leishmaniasis (CL) who resided in an area endemic for Leishmania braziliensis in Brazil were obtained before the initiation of antileishmanial treatment. Kalazar Detect^(r)(InBios, Seattle, WA) recombinant K39 antigen-based immunochromatographic strips were used according to the manufacturer''s instructions. The test results were evaluated independently by two examiners in sequential order. The positive controls for the test included five serum samples from five patients with parasitologically confirmed diagnosis of VL caused by Leishmania infantum in Brazil. Overall, 100% of the samples obtained from patients with CL were negative, confirming the absence of a serological cross-reaction for individuals with cutaneous disease when these patients were evaluated using the rapid test. The lack of a cross-reaction in patients who were infected by parasites of the same genus highlights the specificity of the rK39 antigen for the diagnosis of VL in areas with the sympatric circulation of L. braziliensis and L. infantum.     

Diagnostic accuracy of direct agglutination test,rK39 ELISA and six rapid diagnostic tests among visceral leishmaniasis patients with and without HIV coinfection in Ethiopia

Diagnosis of a first-time visceral leishmaniasis (VL) infection in Ethiopia is established by use of a rapid diagnostic test (RDT) detecting antibodies against rK39, direct agglutination test (DAT) and microscopy according to the national algorithm. The performance of individual tests and algorithm is variable and depends on several factors, one being HIV status. Limited data are available on the performance of tests in VL-HIV coinfected patients.Assessment of the performance of DAT (ITM-A), rK39 ELISA (Serion) and six RDT (Onsite Leishmania Ab CTK, Antigen ICT Xinjier, IT Leish Biorad, Kalazar Detect Inbios, rK39 IgG1 Coris, rk28 IgG1 Coris) for the diagnosis of VL was done on a panel of 91 stored serum and plasma samples of ‘first-episode’ suspected VL patients, with HIV coinfection (n = 51) and without (n = 40). A combined reference standard was used: either positive microscopy on tissue aspirates, or in case of negative microscopy, positive PCR results on the aspirate slide. Additionally, endemic healthy controls (n = 20), non-endemic controls (n = 10) and patients with confirmed malaria infection (n = 10) were tested for specificity evaluation. Sensitivities ranged from 69.2% for DAT (applied cut-off ≥ 1/3200) to 92.2% for the Onsite RDT, whereas specificities ranged from 20.0% for Kalazar Antigen ICT to 100% for IT Leish and rK39 IgG1. Sensitivities from all assays decreased upon stratification according to HIV status but was only significantly different for rK39 Serion ELISA (p-value 0.0084) and the Onsite RDT (p-value 0.0159).In conclusion, performance of commercially available assays for VL on samples from Northern-Ethiopian patients varied widely with a substantial decrease in sensitivity in the VL-HIV coinfected group. Clear guidelines on minimal performance criteria of individual tests and algorithms are needed, as well as which reference standard should be used to determine the performance.