Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.23.5 (cathepsin D)
 4,130 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two new inhibitors, 4 and 5, of the aspartic proteinase porcine pepsin were synthesized. These compounds, which span the P4-P'3 binding subsites of the enzyme, were derived by replacing the Nph-Phe dipeptidyl unit of a good pepsin substrate, H2N-Phe-Gly-His-Nph-Phe-Ala-Phe-OMe (3), with statine [(3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid, Sta]. Hexapeptide 5, H2N-Phe-Gly-Val-(S,S)-Sta-Ala-Phe-OMe, is an extremely potent inhibitor of pepsin with a Ki value less than 1 nM. This result is consistent with the proposal that statine functions as a bioisosteric replacement for a substrate dipeptidyl unit. Compound 4, which contains His at P2, is 2 orders of magnitude less active than the valine analogue 5 (Ki = 150 nM). The factor for the decrease in binding to pepsin effected by replacement of Val by His at P2 parallels the ratio of protonated vs unprotonated imidazole group in peptide 4 at pH 4, according to the Henderson-Hasselbach equation. This result suggests that a positively charged side chain at P2 is undesirable for maximum pepsin inhibition. Kinetic constants for several known inhibitors of pepsin and renin are presented that demonstrate that the effect of His incorporation at P2 on pepsin inhibition depends upon the peptide sequence and that the effect is considerably different for renin inhibitors. We further suggest that the high selectivity of potent renin inhibitors known to be only weak pepsin and cathepsin D inhibitors is due in part to the extent of histidine protonation at P2 arising from pH differences in the inhibition kinetics assay of renin (neutral conditions) compared to other aspartic proteinases (acid pH 2-4).
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PMID:Inhibition of porcine pepsin by two substrate analogues containing statine. The effect of histidine at the P2 subsite on the inhibition of aspartic proteinases. 312 96

The substrate specificity of porcine pepsin has been altered by site-directed mutagenesis in an attempt to selectively cleave bovine hide collagen at only a few sites, similar to cathepsin D, for the production of high quality gelatin. Kinetic parameters were determined using chromogenic peptide substrates based on the sequence Lys-Pro-Xaa-Yaa-Phe*Nph-Arg-Leu (where Xaa is Ile or Pro, Yaa is Glu. Leu, Gln or Lys, Nph is p-nitrophenylalanine, and * is the site of cleavage). Substitution of Thr222 and Glu287 within the S2 subsite of pepsin by Val and Met, respectively, produced a double mutant with a two- to fourfold higher kcat/Km, compared with wild-type pepsin, for the chromogenic peptides with residues Leu, Gln, and Glu at position P2 (Yaa). The results suggest that the functional group of the P2 side chain may be exposed to solvent, while the aliphatic portion interacts with hydrophobic residues comprising S2. Wild-type pepsin cleaved a peptide corresponding to the carboxy-terminal telopeptide region of bovine type I collagen alpha1 chain, SGGYDLSFLPQPPQE, predominantly at three sites (Asp-Leu, Leu-Ser, and Phe-Leu) and at a significantly lower rate at Ser-Phe. However, Thr222Val/Glu287Met cleaved site Ser-Phe at a rate 20-fold higher than the wild-type. Significantly, enzymes containing the double substitution Phe111Thr/Leu112Phe cleaved this peptide predominantly at one site Leu-Ser (similar to cathepsin D) and at a rate 23-fold higher than the wild-type. These mutants can potentially enhance the rate of solubilization of bovine hide collagen under conditions mild enough to maintain the triple helix structure and hence minimize the rate of subsequent denaturation and proteolytic cleavage.
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PMID:Modification of the substrate specificity of porcine pepsin for the enzymatic production of bovine hide gelatin. 1110 68