Characterization of the Substrate Specificity of Human Carboxypeptidase A4 and Implications for a Role in Extracellular Peptide Processing
摘要:
CPA4 (carboxypeptidase A4) is a member of the metallocarboxypeptidase family. CPA4 was originally found in a screen of mRNAs up-regulated by sodium butyrate-induced differentiation of cancer cells. Further studies suggested a relation between CPA4 and prostate cancer aggressiveness. In the present study, we determined that CPA4 is secreted from cells as a soluble proenzyme (pro-CPA4) that can be activated by endoproteases, such as trypsin. Three complementary approaches were used to study the substrate specificity of CPA4; kinetic analysis was performed using a new series of chromogenic substrates and some biologically relevant peptides, the cleavage of synthetic peptides was tested individually, and the cleavage of a mixture of > 100 mouse brain peptides was examined using a quantitative peptidomics mass spectrometry-based approach. CPA4 was able to cleave hydrophobic C-terminal residues with a preference for Phe, Leu, Ile, Met, Tyr, and Val. However, not all peptides with C-terminal hydrophobic residues were cleaved, indicating the importance of additional residues within the peptide. Aliphatic, aromatic, and basic residues in the P1 position have a positive influence on the cleavage specificity. In contrast, acidic residues, Pro, and Gly have a negative influence in the P1 position. Some of the peptides identified as CPA4 substrates (such as neurotensin, granins, and opioid peptides) have been previously shown to function in cell proliferation and differentiation, potentially explaining the link between CPA4 and cancer aggressiveness. Taken together, these studies suggest that CPA4 functions in neuropeptide processing and regulation in the extracellular environment.
The effect of high pressure on peptide formation by the catalysis of carboxypeptidaseY (substitution of ester or peptide by amino acid derivative) or by thermolysin (condensation of N-acylamino acid and amino acid amide) was studied. The carboxypeptidase Y-catalyzed substitution reaction of N-[3-(2-furyl)acryloyl]phenylalanine ethyl ester with glycinamide or phenylalaninamide showed a six-fold higher
Peptideformation from an N-acyl amino acid ester and an amino acid amide using carboxypeptidase Y as a catalyst was shown to be considerably influenced by applying high pressure; at 150 MPa the peptide yield was almost five-fold higher than that at 0.1 MPa when PheNH2 was used as the nucleophile.
activity on these substrates. On the contrary, carboxypeptidase Y gave Fua-amino acids and Fua-dipeptides as products, depending on the structure of the substrates. Accordingly, liberations of free amino acids were detected in some cases. This result shows that the yeast enzyme acts on some of the substrates in a two step manner: First by amidase and second by a carboxypeptidase activity. Based on
Dipeptide synthesis from N-[3-(2-furyl)acryloyl]-acylated (Fua-) amino acid ethyl ester and amino acid amide catalyzed by wheat bran carboxypeptidase (carboxypeptidase W) was studied. The optimum pH for peptide formation was at pH 8; more than 60% of the initial N-Fua-l-phenylalanine ethyl ester was converted to N-Fua-l-phenylalanylglycinamide under optimum conditions. The dependence of peptide formation on the concentration of amino acid amide showed an apparent saturation; this could be successfully explained by a reaction scheme which involved an acylated enzyme attacked by an enzyme-bound amine. The results for a reaction in the presence of two different amine components also supported this mechanism. Gly–NH2 had a better affinity to the acylated carboxypeptidase and the apparent dissociation constant (KN(app)) was about 50 mM. These results were compared with those for those reactions catalyzed by carboxypeptidases from yeast and malt.