Investigation of a role for Glu-331 and Glu-305 in substrate binding of tripeptidyl-peptidase II

The aim of this study was to investigate the mechanism by which tripeptidyl-peptidase II (TPP II) can specifically release tripeptides from the free N-terminus of an oligopeptide. The subtilisin-like N-terminal part of TPP II was modelled using subtilisin as template. Two glutamate residues (Glu-305 and Glu-331) appeared to be positioned so as to interact with the positively charged N-terminus of the substrate. In order to test this potential interaction, both residues were replaced by glutamine and lysine. The catalytic efficiency was reduced 400-fold for the E331Q variant and 20000-fold for the E331K variant, compared with the wild-type (wt). A substantial part of this reduction was due to decreased substrate affinity, since the K(M) for both mutants was at least two orders of magnitude greater than for the wt. This decrease was linked specifically to interaction with the free N-terminal amino group, based on inhibition studies. Glu-305 appears to be essential for enzymatic activity, but the extremely low activity of the E305Q variant prevented an investigation of the involvement of Glu-305 in substrate binding. The present work is, to our knowledge, the first report to investigate a mechanism for a tripeptidyl-peptidase activity through site-directed mutagenesis.     

Alanine scanning mutagenesis of the prototypic cyclotide reveals a cluster of residues essential for bioactivity

The cyclotides are stable plant-derived mini-proteins with a topologically circular peptide backbone and a knotted arrangement of three disulfide bonds that form a cyclic cystine knot structural framework. They display a wide range of pharmaceutically important bioactivities, but their natural function is in plant defense as insecticidal agents. To determine the influence of individual residues on structure and activity in the prototypic cyclotide kalata B1, all 23 non-cysteine residues were successively replaced with alanine. The structure was generally tolerant of modification, indicating that the framework is a viable candidate for the stabilization of bioactive peptide epitopes. Remarkably, insecticidal and hemolytic activities were both dependent on a common, well defined cluster of hydrophilic residues on one face of the cyclotide. Interestingly, this cluster is separate from the membrane binding face of the cyclotides. Overall, the mutagenesis data provide an important insight into cyclotide biological activity and suggest that specific self-association, in combination with membrane binding mediates cyclotide bioactivities.     

Identification of a new urate and high affinity nicotinate transporter, hOAT10 (SLC22A13)

The orphan transporter hORCTL3 (human organic cation transporter like 3; SLC22A13) is highly expressed in kidneys and to a weaker extent in brain, heart, and intestine. hORCTL3-expressing Xenopus laevis oocytes showed uptake of [(3)H]nicotinate, [(3)H]p-aminohippurate, and [(14)C]urate. Hence, hORCTL3 is an organic anion transporter, and we renamed it hOAT10. [(3)H]Nicotinate transport by hOAT10 into X. laevis oocytes and into Caco-2 cells was saturable with Michaelis constants (K(m)) of 22 and 44 microm, respectively, suggesting that hOAT10 may be the molecular equivalent of the postulated high affinity nicotinate transporter in kidneys and intestine. The pH dependence of hOAT10 suggests p-aminohippurate(-)/OH(-), urate(-)/OH(-), and nicotinate(-)/OH(-) exchange as possible transport modes. Urate inhibited [(3)H]nicotinate transport by hOAT10 with an IC(50) value of 759 microm, assuming that hOAT10 represents a low affinity urate transporter. hOAT10-mediated [(14)C]urate uptake was elevated by an exchange with l -lactate, pyrazinoate, and nicotinate. Surprisingly, we have detected urate(-)/glutathione exchange by hOAT10, consistent with an involvement of hOAT10 in the renal glutathione cycle. Uricosurics, diuretics, and cyclosporine A showed substantial interactions with hOAT10, of which cyclosporine A enhanced [(14)C]urate uptake, providing the first molecular evidence for cyclosporine A-induced hyperuricemia.     

Structure of the R3/I5 chimeric relaxin peptide, a selective GPCR135 and GPCR142 agonist

The human relaxin family comprises seven peptide hormones with various biological functions mediated through interactions with G-protein-coupled receptors. Interestingly, among the hitherto characterized receptors there is no absolute selectivity toward their primary ligand. The most striking example of this is the relaxin family ancestor, relaxin-3, which is an agonist for three of the four currently known relaxin receptors: GPCR135, GPCR142, and LGR7. Relaxin-3 and its endogenous receptor GPCR135 are both expressed predominantly in the brain and have been linked to regulation of stress and feeding. However, to fully understand the role of relaxin-3 in neurological signaling, the development of selective GPCR135 agonists and antagonists for in vivo studies is crucial. Recent reports have demonstrated that such selective ligands can be achieved by making chimeric peptides comprising the relaxin-3 B-chain combined with the INSL5 A-chain. To obtain structural insights into the consequences of combining A- and B-chains from different relaxins we have determined the NMR solution structure of a human relaxin-3/INSL5 chimeric peptide. The structure reveals that the INSL5 A-chain adopts a conformation similar to the relaxin-3 A-chain, and thus has the ability to structurally support a native-like conformation of the relaxin-3 B-chain. These findings suggest that the decrease in activity at the LGR7 receptor seen for this peptide is a result of the removal of a secondary LGR7 binding site present in the relaxin-3 A-chain, rather than conformational changes in the primary B-chain receptor binding site.     

The A-chain of human relaxin family peptides has distinct roles in the binding and activation of the different relaxin family peptide receptors

The relaxin peptides are a family of hormones that share a structural fold characterized by two chains, A and B, that are cross-braced by three disulfide bonds. Relaxins signal through two different classes of G-protein-coupled receptors (GPCRs), leucine-rich repeat-containing GPCRs LGR7 and LGR8 together with GPCR135 and GPCR142, now referred to as the relaxin family peptide (RXFP) receptors 1-4, respectively. Although key binding residues have been identified in the B-chain of the relaxin peptides, the role of the A-chain in their activity is currently unknown. A recent study showed that INSL3 can be truncated at the N terminus of its A-chain by up to 9 residues without affecting the binding affinity to its receptor RXFP2 while becoming a high affinity antagonist. This suggests that the N terminus of the INSL3 A-chain contains residues essential for RXFP2 activation. In this study, we have synthesized A-chain truncated human relaxin-2 and -3 (H2 and H3) relaxin peptides, characterized their structure by both CD and NMR spectroscopy, and tested their binding and cAMP activities on RXFP1, RXFP2, and RXFP3. In stark contrast to INSL3, A-chain-truncated H2 relaxin peptides lost RXFP1 and RXFP2 binding affinity and concurrently cAMP-stimulatory activity. H3 relaxin A-chain-truncated peptides displayed similar properties on RXFP1, highlighting a similar binding mechanism for H2 and H3 relaxin. In contrast, A-chain-truncated H3 relaxin peptides showed identical activity on RXFP3, highlighting that the B-chain is the sole determinant of the H3 relaxin-RXFP3 interaction. Our results provide new insights into the action of relaxins and demonstrate that the role of the A-chain for relaxin activity is both peptide- and receptor-dependent.     

Non-infected preterm parturition is related to increased concentrations of IL-6, IL-8 and MCP-1 in human cervix

Background  

Human cervical ripening is an inflammatory process. In labour at term the mRNA-levels and protein concentrations for interleukin-6 (IL-6) and IL-8 in cervix significantly increase. The aim of this study was to investigate if there are differences in the inflammatory process of preterm and term cervical ripening.     

Mercapturic acids of acrylamide and glycidamide as biomarkers of the internal exposure to acrylamide in the general population

Acrylamide (AA), a widely used industrial monomer which is categorised to be carcinogenic, was found to be generated in starch-containing foods during the heating process. This discovery has caused reasonable concern about possible health risks to humans due to dietary acrylamide uptake. In order to gain more information on human metabolism of acrylamide and to contribute to the assessment of the human carcinogenic risk due to AA uptake we measured the mercapturic acid of AA and its epoxide glycidamide (GA) i.e. N-acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA) and N-(R,S)-acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) in human urine. The relation between AAMA and GAMA is important in this context because GA is thought to be the ultimate carcinogenic metabolite of AA. The median levels in smokers (n=13) were found to be about four times higher than in non-smokers (n=16) with median levels of 127 microg/l versus 29 microg/l for AAMA and 19 microg/l versus 5 microg/l for GAMA. Therefore cigarette smoke proved to be an important source of acrylamide exposure. The level of AAMA in the occupationally non-exposed collective (n=29) ranged from 3 to 338 microg/l, the level of GAMA from 相似文献