Proline residues confer unique structural constraints on peptide chains and markedly influence the susceptibility of proximal peptide bonds to protease activity. This review presents a critical analysis of peptidases involved in the cleavage of proline-containing peptide bonds, with particular attention to the role of proline peptidases in the regulation of the lifetime of biologically active peptides. Peptidases discussed include aminopeptidase P, prolidase, dipeptidyl peptidase IV, prolyl endopeptidase, and prolyl iminopeptidase. Attention is also given to HIV-1 protease, because this key enzyme processes an Xaa-Pro peptide bond. Analysis of the above enzymes reveals that they may function as key pacemakers in the control of the activity of many peptide hormones and that they are involved in a variety of immunological processes, including T-cell-mediated immune response. The novel occurrence of cis-trans isomerization about Xaa-Pro bonds and the biological function of peptidyl-prolyl cis-trans i...

Proline-Dependent Structural and Biological Properties of Peptides and Proteins

Dipeptidyl peptidase IV (DPP-IV), assigned to the CD26 cluster, is expressed on epithelial cells and lymphocytes and is a multifunctional or pleiotropic protein. Its peptidase activity causes degradation of many biologically active peptides, e.g. some incretins secreted by the enteroendocrine system. DPP-IV has, therefore, become a novel therapeutic target for inhibitors that extend endogenously produced insulin half-life in diabetics, and several reviews have appeared in recent months concerning the clinical significance of CD26/DPP-IV. Biological fluids contain relatively high levels of soluble CD26 (sCD26). The physiological role of sCD26 and its relation, if any, to CD26 functions, remain poorly understood because whether the process for CD26 secretion and/or shedding from cell membranes is regulated or not is not known. Liver epithelium and lymphocytes are often cited as the most likely source of sCD26. It is important to establish which tissue or organ is the protein source as well as the circumstances that can provoke an abnormal presence/absence or altered levels in many diseases including cancer, so that sCD26 can be validated as a clinical marker or a therapeutic target. For example, we have previously reported low levels of sCD26 in the blood of colorectal cancer patients, which indicated the potential usefulness of the protein as a biomarker for this cancer in early diagnosis, monitoring and prognosis. Through this review, we envisage a role for sCD26 and the alteration of normal peptidase capacity (in clipping enteroendocrine or other peptides) in the complex crosstalk between the lymphoid lineage and, at least, some malignant tumours.

On the origin of serum CD26 and its altered concentration in cancer patients

Lung endothelial dipeptidyl peptidase IV promotes adhesion and metastasis of rat breast cancer cells via tumor cell surface-associated fibronectin

The CD26 antigen, one of the major costimulatory molecules in T cell activation, was shown to possess dipeptidyl peptidase IV (DPP IV) activity. Previously, we demonstrated that immunosuppressed kidney transplant patients exhibit lower DPP IV serum activity as compared with healthy individuals. In the present study, we analyzed the role of CD26/DPP IV in the immune cascade triggered by organ transplantation and leading to acute rejection of cardiac allografts in rat recipients. Transplantation of hearts from (Lewis × Brown Norway)F1 donors into Lewis hosts resulted in an early (24 hr) increase in cellular CD26 expression, followed by a rise in DPP IV serum activity, which peaked at day 6, i.e., before the time of actual graft loss. Specific targeting of DPP IV activity with a novel, low-molecular-weight inhibitor of the diphenyl-phosphonate group (prodipine) abrogated acute rejection and prolonged cardiac allograft survival to 14.0±0.9 days (P

Inhibition of CD26/dipeptidyl peptidase IV activity in vivo prolongs cardiac allograft survival in rat recipients

Glucagon-like peptide-1 (GLP-1) receptor agonism or DPP-4 inhibition does not accelerate neoplasia in carcinogen treated mice.

A new fluorometric assay for determining dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) was developed. The synthetic substrate glycyl-L-proline-4-methoxy-2-naphthylamide (20 mmol/L), Tris buffer (50 mmol/L, pH 8.3), and serum (20 microL) are mixed and incubated. The reaction is stopped with citrate (100 mmol/L, pH 4.0) and the released 4-methoxy-2-naphthylamine is measured fluorometrically. The mean value of DPP IV activity in serum for 64 healthy subjects was 58 (SD 16) mumol of 4-methoxy-2-naphthylamine released per liter of serum per minute. The proposed procedure is sensitive, rapid, and accurate and can easily be automated.

Assay of dipeptidyl peptidase IV in serum by fluorometry of 4-methoxy-2-naphthylamine.

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Assay of dipeptidyl peptidase IV in serum by fluorometry of 4-methoxy-2-naphthylamine.