1. Biodegradation of Nodularin by a Microcystin-Degrading Bacterium: Performance, Degradation Pathway, and Potential Application
Mengxuan Yuan, Qin Ding, Rongli Sun, Juan Zhang, Lihong Yin, Yuepu Pu Toxins (Basel). 2021 Nov 18;13(11):813. doi: 10.3390/toxins13110813.
Currently, studies worldwide have comprehensively recognized the importance of Sphingomonadaceae bacteria and the mlrCABD gene cluster in microcystin (MC) degradation. However, knowledge about their degradation of nodularin (NOD) is still unclear. In this study, the degradation mechanism of NOD by Sphingopyxis sp. m6, an efficient MC degrader isolated from Lake Taihu, was investigated in several aspects, including degradation ability, degradation products, and potential application. The strain degraded NOD of 0.50 mg/L with a zero-order rate constant of 0.1656 mg/L/d and a half-life of 36 h. The average degradation rate of NOD was significantly influenced by the temperature, pH, and initial toxin concentrations. Moreover, four different biodegradation products, linear NOD, tetrapeptide H-Glu-Mdhb-MeAsp-Arg-OH, tripeptide H-Mdhb-MeAsp-Arg-OH, and dipeptide H-MeAsp-Arg-OH, were identified, of which the latter two are the first reported. Furthermore, the four mlr genes were upregulated during NOD degradation. The microcystinase MlrA encoded by the mlrA gene hydrolyzes the Arg-Adda bond to generate linear NOD as the first step of NOD biodegradation. Notably, recombinant MlrA showed higher degradation activity and stronger environmental adaptability than the wild strain, suggesting future applications in NOD pollution remediation. This research proposes a relatively complete NOD microbial degradation pathway, which lays a foundation for exploring the mechanisms of NOD degradation by MC-degrading bacteria.
2. New insight into the binding mode of peptides at urotensin-II receptor by Trp-constrained analogues of P5U and urantide
Alfonso Carotenuto, et al. J Pept Sci. 2013 May;19(5):293-300. doi: 10.1002/psc.2498. Epub 2013 Mar 25.
Urotensin II (U-II) is a disulfide bridged peptide hormone identified as the ligand of a G-protein-coupled receptor. Human U-II (H-Glu-Thr-Pro-Asp-c[Cys-Phe-Trp-Lys-Tyr-Cys]-Val-OH) has been described as the most potent vasoconstrictor compound identified to date. We have recently identified both a superagonist of human U-II termed P5U (H-Asp-c[Pen-Phe-Trp-Lys-Tyr-Cys]-Val-OH) and the compound termed urantide (H-Asp-c[Pen-Phe-D-Trp-Orn-Tyr-Cys]-Val-OH), which is the most potent UT receptor peptide antagonist described to date. In the present study, we have synthesized four analogues of P5U and urantide in which the Trp(7) residue was replaced by the highly constrained L-Tpi and D-Tpi residues. The replacement of the Trp(7) by Tpi led to active analogues. Solution NMR analysis allowed improving the knowledge on conformation-activity relationships previously reported on UT receptor ligands.
3. Unraveling the active conformation of urotensin II
Alfonso Carotenuto, Paolo Grieco, Pietro Campiglia, Ettore Novellino, Paolo Rovero J Med Chem. 2004 Mar 25;47(7):1652-61. doi: 10.1021/jm0309912.
Urotensin II (U-II) is a disulfide-bridged undecapeptide recently identified as the ligand of an orphan G-protein-coupled receptor. Human U-II (H-Glu-Thr-Pro-Asp-cyclo[Cys-Phe-Trp-Lys-Tyr-Cys]-Val-OH) has been described as the most potent vasoconstrictor compound identified to date. With the aim of elucidating the active conformation of hU-II, we have performed a spectroscopic analysis of hU-II minimal active fragment hU-II(4-11) in different environmental conditions. The analysis indicated that hU-II(4-11) was highly structured in the anisotropic membrane mimetic SDS solution, showing a type II' beta-turn structure, which is almost unprecedented for L-amino acid peptides. Micelle bound structure of hU-II(4-11) was then compared with those of four synthetic analogues recently synthesized in our lab, bearing modified Cys residues at position 5 and/or position 10 and characterized by different levels of agonist activity. The structures of the active compounds were found to be very similar to that of hU-II(4-11), while a barely active compound does not show any propensity to beta-turn formation. Furthermore, distances among putative pharmacophoric points in the structures of the active compounds obtained in SDS solution are in good agreement with those found in a recently described non-peptide agonist of the hU-II receptor. A type II' beta-turn structure was already found for the somatostatin analogue octreotide. On the basis of the similarity of the primary and 3D structures of U-II and somatostatin analogues and on the basis of the sequence homology between the GPR14/UT-II receptor and members of the somatostatin receptor family, a common evolutionary pathway for the signal transmission system activated by these peptide can be hypothesized.
