Mass spectrometry assisted assignments of binding and cleavage sites of copper(II) and platinum(II) complexes towards oxidized insulin B chain

Selective hydrolysis of oxidized insulin chain B by a Zr(IV)-substituted Wells-Dawson polyoxometalate

We report for the first time on the selective hydrolysis of a polypeptide system by a metal-substituted polyoxometalate (POM). Oxidized insulin chain B, a 30 amino acid polypeptide, was selectively cleaved by the Zr(IV)-substituted Wells-Dawson POM, K15H[Zr(α2-P2W17O61)2]·25H2O, under physiological pH and temperature conditions in aqueous solution. HPLC-ESI-MS, LC-MS/MS, MALDI-TOF and MALDI-TOF MS/MS data indicate hydrolysis at the Phe1-Val2, Gln4-His5, Leu6-Cys(SO3H)7, and Gly8-Ser9 peptide bonds. The rate of oxidized insulin chain B hydrolysis (0.45 h(-1) at pH 7.0 and 60 °C) was calculated by fitting the integration values of its HPLC-UV signal to a first-order exponential decay function. (1)H NMR measurements show significant line broadening and shifting of the polypeptide resonances upon addition of the Zr(IV)-POM, indicating that interaction between the Zr(IV)-POM and the polypeptide takes place in solution. Circular dichroism (CD) measurements clearly prove that the flexible unfolded nature of the polypeptide was retained in the presence of the Zr(IV)-POM. The thermal stability of the Zr(IV)-POM in the presence of the polypeptide chain during the hydrolytic reaction was confirmed by (31)P NMR spectroscopy. Despite the highly negative charge of the Zr(IV)-POM, the mechanism of interaction appears to be dominated by a strong metal-directed binding between the positively charged Zr(IV) center and negatively charged amino acid side chains.

Biological control of wheat root diseases by the CLP-producing strain Pseudomonas fluorescens HC1-07

Pseudomonas fluorescens HC1-07, previously isolated from the phyllosphere of wheat grown in Hebei province, China, suppresses the soilborne disease of wheat take-all, caused by Gaeumannomyces graminis var. tritici. We report here that strain HC1-07 also suppresses Rhizoctonia root rot of wheat caused by Rhizoctonia solani AG-8. Strain HC1-07 produced a cyclic lipopeptide (CLP) with a molecular weight of 1,126.42 based on analysis by electrospray ionization mass spectrometry. Extracted CLP inhibited the growth of G. graminis var. tritici and R. solani in vitro. To determine the role of this CLP in biological control, plasposon mutagenesis was used to generate two nonproducing mutants, HC1-07viscB and HC1-07prtR2. Analysis of regions flanking plasposon insertions in HC1-07prtR2 and HC1-07viscB revealed that the inactivated genes were similar to prtR and viscB, respectively, of the well-described biocontrol strain P. fluorescens SBW25 that produces the CLP viscosin. Both genes in HC1-07 were required for the production of the viscosin-like CLP. The two mutants were less inhibitory to G. graminis var. tritici and R. solani in vitro and reduced in ability to suppress take-all. HC1-07viscB but not HC-07prtR2 was reduced in ability to suppress Rhizoctonia root rot. In addition to CLP production, prtR also played a role in protease production.

Ion mobility-mass spectrometry study of folded ubiquitin conformers induced by treatment with cis-[Pd(en)(H2O2]2+

Ion mobility-mass spectrometry is used to study the new conformers of bovine ubiquitin (Ub) and the palladium(II) binding sites after the incubation with cis-[Pd(en)(H(2)O)(2)](2+) where en = ethylenediamine. Palladium(II) complexes are potentially useful proteomic reagents because they selectively bind to the side groups of methionine and histidine and hydrolytically cleave the peptide bond. Incubating 1.0 mM solution of Ub with 10.0 molar excess of cis-[Pd(en)(H(2)O)(2)](2+) results with one to four Pd(2+) or Pd(en)(2+) being attached to intact Ub and two conformer families at each of the 4+ to 11+ charge states. The 4+ and 5+ species exhibit a compact form, which is also observed in untreated Ub, and a new highly folded conformer. The 6+ to 10+ exhibit an elongated form, also observed in Ub, and a new partially folded conformer. The new conformers are shown to be more stable if they contain at least one Pd(2+), rather than all Pd(en)(2+). IM-MS/MS of [UbPd(2)en+5H](9+) shows that both the partially folded and elongated conformers first lose the en ligand, followed by dissociating into product ions that indicate that Met1, Glu51/Asp52, His68, and Glu16 are binding sites for Pd(2+). These results suggest that Pd(2+) is simultaneously binding to multiple side groups across different regions of Ub. This type of sequestering of Pd(2+) probably reduces the efficiency of Pd(2+) ions to selectively cleave Ub because it prevents Pd(2+) anchoring to only Met or His and to an adjacent backbone amide nitrogen and forming the "activated complex" necessary for specific peptide bond cleavage.