Specific calpain activity evaluation in Plasmodium parasites.

In the intraerythrocytic trophozoite stages of Plasmodium falciparum, the calcium-dependent cysteine protease calpain (Pf-calpain) has an important role in the parasite calcium modulation and cell development. We established specific conditions to follow by confocal microscopy and spectrofluorimetry measurements the intracellular activity of Pf-calpain in live cells. The catalytic activity was measured using the fluorogenic Z-Phe-Arg-MCA (where Z is carbobenzoxy and MCA is 4-methylcoumaryl-7-amide). The calmodulin inhibitor calmidazolium and the sarcoplasmic reticulum calcium ATPase inhibitor thapsigargin were used for modifications in the cytosolic calcium concentrations that persisted in the absence of extracellular calcium. The observed calcium-dependent peptidase activity was greatly inhibited by specific cysteine protease inhibitor E-64 and by the selective calpain inhibitor ALLN (N-acetyl-l-leucyl-l-leucyl-l-norleucinal). Taken together, we observed that intracellular Pf-calpain can be selectively detected and is the main calcium-dependent protease in the intraerythrocytic stages of the parasite. The method described here can be helpful in cell metabolism studies and antimalarial drug screening.

Substrate specificity studies of the cysteine peptidases falcipain-2 and falcipain-3 from Plasmodium falciparum and demonstration of their kininogenase activity.

We studied the substrate specificity requirements of recombinant cysteine peptidases from Plasmodium falciparum, falcipain-2 (FP-2) and falcipain-3 (FP-3), using fluorescence resonance energy transfer (FRET) peptides as substrates. Systematic modifications were introduced in the lead sequence Abz-KLRSSKQ-EDDnp (Abz=ortho-aminobenzoic acid; EDDnp=N-[2,4-dinitrophenyl]ethylenediamine) resulting in five series assayed to map S3-S'2 subsite specificity. Despite high sequence identity and structural similarity between FP-2 and FP-3, noteworthy differences in substrate specificity were observed. The S1 subsite of FP-2 preferentially accommodates peptides containing the positively charged residue Arg in P1, while FP-3 has a clear preference for the hydrophobic residue Leu in this position. The S2 subsite of FP-2 and FP-3 presents a strict specificity for hydrophobic residues, with Leu being the residue preferred by both enzymes. FP-2 did not show preference for the residues present at P3, while FP-3 hydrolysed the peptide Abz-ALRSSRQ-EDDnp, containing Ala at P3, with the highest catalytic efficiency of all series studied. FP-2 has high susceptibility for substrates containing hydrophobic residues in P'1, while FP-3 accommodates well peptides containing Arg in this position. The S'2 subsite of both enzymes demonstrated broad specificity. In addition, radioimmunoassay experiments indicated that kinins can be generated by FP-2 and FP-3 proteolysis of high molecular weight kininogen (HK). Both enzymes excised Met-Lys-bradykinin, Lys-bradykinin and bradykinin from the fluorogenic peptide Abz-MISLMKRPPGFSPFRSSRI-NH2, which corresponds to the Met(375) to Ile(393) sequence of HK. The capability of FP-2 and FP-3 to release kinins suggests the involvement of these enzymes in the modulation of malaria pathophysiology.

Production of a His-tagged canecystatin in transgenic sugarcane and subsequent purification.

Transgenic plants have been used widely as expression systems of recombinant proteins in recent years. This process can be an efficient alternative for the large-scale production of proteins. In this work, we present the establishment of transgenic sugarcane expressing a His-tagged canecystatin under the control of the maize ubiquitin promoter. A number of studies have demonstrated that cystatins, which are natural inhibitors of cysteine proteinases, can be used for protection against insect attacks. A transformed sugarcane plant that presented high levels of (HIS)CaneCPI-1 expression, was selected for the purification of this protein through affinity chromatography in a nickel column. This purified (HIS)CaneCPI-1 was immunodetected using a polyclonal antibody, which was also able to detect the (HIS)CaneCPI-1 in a crude extract from transgenic plant leaves. Assays of inhibitory activity performed with the purified (HIS)CaneCPI-1 revealed its ability to inhibit the catalytic activity of midgut cysteine proteinase partially purified from the sugarcane weevil Sphenophorus levis and human cathepsin L in nanomolar order. These studies demonstrate that sugarcane is a viable expression system for recombinant protein production.

An unexpected inhibitory activity of Kunitz-type serine proteinase inhibitor derived from Boophilus microplus trypsin inhibitor on cathepsin L.

Several BPTI-Kunitz-type serine proteinase inhibitors were described in tick Boophilus microplus and Rhipicephalus sanguineus species. In this work, we present a synthetic gene based on two tick BPTI-Kunitz-type serine proteinase inhibitors, the first domain of B. microplus trypsin inhibitor-A (BmTI-A) and the carrapatin, the inhibitors were named BmTIsint and BmTIsint Mut. Our present results showed that BmTIsint and BmTIsint Mut inhibited trypsin (K(i) 3.3 and 1.0 nM) and human plasma kallikrein (K(i) 16.5 and 35 nM), but in contrast to BmTI-A, the inhibitors did not inhibit human neutrophil elastase. BmTIsint was able to produce immunological response in mice but not in bovines. In addition, it is the first description of a BPTI-Kunitz-type inhibitor as a cysteine proteinase inhibitor, BmTIsint apparent dissociation constant (K(i)) for cathepsin L was 108 nM. Our findings open the possibility up to obtain new molecules as potent serine or cysteine proteinase inhibitors using BmTIsint as a model.

Recombinant human cathepsin X is a carboxymonopeptidase only: a comparison with cathepsins B and L.

The S1 and S2 subsite specificity of recombinant human cathepsins X was studied using fluorescence resonance energy transfer (FRET) peptides with the general sequences Abz-Phe-Xaa-Lys(Dnp)-OH and Abz-Xaa-Arg-Lys(Dnp)-OH, respectively (Abz=ortho-aminobenzoic acid and Dnp=2,4-dinitrophenyl; Xaa=various amino acids). Cathepsin X cleaved all substrates exclusively as a carboxymonopeptidase and exhibited broad specificity. For comparison, these peptides were also assayed with cathepsins B and L. Cathepsin L hydrolyzed the majority of them with similar or higher catalytic efficiency than cathepsin X, acting as an endopeptidase mimicking a carboxymonopeptidase (pseudo-carboxymonopeptidase). In contrast, cathepsin B exhibited poor catalytic efficiency with these substrates, acting as a carboxydipeptidase or an endopeptidase. The S1' subsite of cathepsin X was mapped with the peptide series Abz-Phe-Arg-Xaa-OH and the enzyme preferentially hydrolyzed substrates with hydrophobic residues in the P1' position.

Comparative substrate specificity analysis of recombinant human cathepsin V and cathepsin L.

Cathepsins V and L have high identity and few structural differences. In this paper, we reported a comparative study of the hydrolytic activities of recombinant human cathepsins V and L using fluorescence resonance energy transfer peptides derived from Abz-KLRSSKQ-EDDnp (Abz = ortho-aminobenzoic acid and EDDnp = N-(2,4-dinitrophenyl)ethylenediamine). Five series of peptides were synthesized to map the S3 to S2' subsites. The cathepsin V subsites S1 and S3 present a broad specificity while cathepsin L has preference for positively charged residues. The S2 subsites of both enzymes require hydrophobic residues with preference for Phe and Leu. The S1' and S2' subsites of cathepsins V and L are less specific. Based on these data we designed substrates to explore the electrostatic potential differences of them. Finally, the kininogenase activities of these cathepsins were compared using synthetic human kininogen fragments. Cathepsin V preferentially released Lys-bradykinin while cathepsin L released bradykinin. This kininogenase activity by cathepsins V and L was also observed from human high and low molecular weight kininogens.

Inhibitory selectivity of canecystatin: a recombinant cysteine peptidase inhibitor from sugarcane.

The cDNA of a cystein peptidase inhibitor was isolated from sugarcane and expressed in Escherichia coli. The protein, named canecystatin, has previously been shown to exert antifungal activity on the filamentous fungus Trichoderma reesei. Herein, the inhibitory specificity of canecystatin was further characterized. It inhibits the cysteine peptidases from plant source papain (Ki =3.3nM) and baupain (Ki=2.1x10(-8)M), but no inhibitory effect was observed on ficin or bromelain. Canecystatin also inhibits lysosomal cysteine peptidases such as human cathepsin B (Ki=125nM), cathepsin K (Ki=0.76nM), cathepsin L (Ki=0.6nM), and cathepsin V (Ki=1.0nM), but not the aspartyl peptidase cathepsin D. The activity of serine peptidases such as trypsin, chymotrypsin, pancreatic, and neutrophil elastases, and human plasma kallikrein is not affected by the inhibitor, nor is the activity of the metallopeptidases angiotensin converting enzyme and neutral endopeptidase. This is the first report of inhibitory activity of a sugarcane cystatin on cysteine peptidases.

Carboxydipeptidase activities of recombinant cysteine peptidases. Cruzain of Trypanosoma cruzi and CPB of Leishmania mexicana.

The recombinant cysteine peptidases, cruzain from Trypanosoma cruzi and CPB2.8DeltaCTE from Leishmania mexicana, are cathepsin L-like and characteristically endopeptidases. In this study, we characterized the carboxydipeptidase activities of these enzymes and compared them with those of human recombinant cathepsin B and cathepsin L. The analysis used the internally quenched fluorescent peptide Abz-FRFK*-OH and some of its analogues, where Abz is ortho-aminobenzoic acid and K* is (2,4-dinitrophenyl)-epsilon-NH2-lysine. These peptides were demonstrated to be very sensitive substrates, due to the strong quenching effect of K* on the fluorescence of the Abz group. The carboxydipeptidase activity of cruzain was shown to be very similar to that of cathepsin B, while that of CPB2.8DeltaCTE is closer to the carboxydipeptidase activity of cathepsin L. The S2 subsite architecture of cruzain and the nature of the amino acid at the P2 position of the substrates determine its carboxydipeptidase activity and gives further and direct support to the notion that the carboxydipeptidase activity of the papain family cysteine peptidases rely on the S2-P2 interaction [Nägler D. K., Tam, W., Storer, A.C., Krupa, J.C., Mort, J.S. & Menard, R. (1999) Biochemistry38, 4868-4874]. Cruzain and CPB2.8DeltaCTE presented a broad pH-range for both the endo- and exo-peptidase activities, although the later is approximately one order of magnitude lower. This feature, that is not common in related mammalian cysteine peptidases, is consistent with the enzymes being exposed to different environmental conditions and having different locations during parasite development.

S3 to S3' subsite specificity of recombinant human cathepsin K and development of selective internally quenched fluorescent substrates.

We have systematically examined the S3 to S3' subsite substrate specificity requirements of cathepsin K using internally quenched fluorescent peptides derived from the lead sequence Abz-KLRFSKQ-EDDnp [where Abz is o -aminobenzoic acid and EDDnp is N -(2,4-dinitrophenyl)ethylenediamine]. We assayed six series of peptides, in which each position except Gln was substituted with various natural amino acids. The results indicated that the S3-S1 subsite requirements are more restricted than those of S1'-S3'. Cathepsin K preferentially accommodates hydrophobic amino acids with aliphatic side chains (Leu, Ile and Val) in the S2 site. Modifications at P1 residues also have a large influence on cathepsin K activity. Positively charged residues (Arg and Lys) represent the best accepted amino acids in this position, although a particular preference for Gly was found as well. Subsite S3 accepted preferentially basic amino acids such as Lys and Arg. A broad range of amino acids was accommodated in the remaining subsites. We further explored the acceptance of a Pro residue in the P2 position by cathepsin K in order to develop specific substrates for the enzyme. Two series of peptides with the general sequences Abz-KXPGSKQ-EDDnp and Abz-KPXGSKQ-EDDnp (where X denotes the position of the amino acid that is altered) were synthesized. The substrates Abz-KPRGSKQ-EDDnp and Abz-KKPGSKQ-EDDnp were cleaved by cathepsin K at the Arg-Gly and Gly-Ser bonds respectively, and have been shown to be specific for cathepsin K when compared with other lysosomal cysteine proteases such as cathepsins L and B and with the aspartyl protease cathepsin D.