The hydroxylase component of soluble methane monooxygenase from Methylococcus capsulatus (Bath) exists in several forms as shown by electrospray-ionisation mass spectrometry.

The hydroxylase of the soluble methane monooxygenase from the bacterium Methylococcus capsulatus (Bath) has been investigated by means of electrospray-ionisation mass spectrometry (ESI-MS) and liquid chromatography ESI-MS (LC/ESI-MS). The hydroxylase is a non-heme diiron protein consisting of three pairs of non-identical subunits (alpha approximately 60 kDa, beta approximately 45 kDa and gamma approximately 20 kDa). Liquid chromatographic separation of the hydroxylase subunits was required before MS analysis in order to detect the alpha-subunit. The masses measured for the three subunits were found to disagree with those calculated from their gene sequences. Experiments involving the use of CNBr and trypsin cleavage followed by LC/ESI-MS and MS/MS analyses permitted the location and correction of errors in the sequences deduced from the use of cDNA. The ESI-MS results also showed that the alpha-subunit of the hydroxylase exists in multiple forms which result from cleavage of the protein. This observation explains a number of enigmatic features of the protein previously reported in the literature and illustrates the pivotal role of ESI-MS in complementing data obtained from molecular biology for the characterisation of the primary sequence of proteins.

Use of electrospray ionization mass spectrometry and tandem mass spectrometry to study binding of F0 inhibitors to ceroid lipofuscinosis protein, a model system for subunit c of mitochondrial ATP synthase.

Ceroid lipofuscinosis protein (CLP), the major accumulating protein in several forms of ceroid lipofuscinosis, has an amino acid sequence that is identical to that of the F0 subunit c of normal bovine ATP synthase. Electrospray ionization mass spectrometry (ESI-MS) has shown that ovine CLP and normal bovine F0 subunit c are identical, including a 42 mass unit post-translational modification. Although the identity and the location of this modification have not been fully established in both species, CLP can be used as a convenient and a unique source of subunit c for studies of F0 inhibitor interactions by ESI-MS analysis. Analysis of mixtures of CLP incubated with several known F0 inhibitors showed that N, N'-dicyclohexylcarbodiimide and organotins bind covalently to CLP but interactions with oligomycin and venturicidin were not observed. The sulphydryl inhibitors, 2,3-dimethoxy-5-methyl-1,4,-benzoquinone (UQ0) and N-ethyl maleimide (NEM) were also shown to bind covalently to the protein. The binding stoichiometry and the relative rate of reaction were then determined for each inhibitor. Tandem mass spectrometry experiments performed on the [M+5H]5+ ion of the intact CLP and of the complexes UQ0-CLP and NEM-CLP allowed the identification of 80% of the CLP sequence and revealed that UQ0 and NEM are both bound to cysteine-64. This work shows the exceptional utility of ESI-MS in studies of the interaction of CLP with a range of inhibitors which are applicable to studies of the F0 component of ATP synthase.

Complete amino acid sequence of the Aa6 subunit of the scorpion Androctonus australis hemocyanin determined by Edman degradation and mass spectrometry.

The primary structure of the hemocyanin Aa6 subunit from the scorpion Androctonus australis was resolved by using protein sequencing and mass spectrometry for analysis of the polypeptide chain and of fragments obtained by CNBr, trypsin, and chymotrypsin cleavage. Due to the high sensitivity of the methodologies used, only a small amount of material, less than 1 mg, was consumed. The complete sequence is composed of 626 amino acid residues and the protein is not glycosylated but probably phosphorylated at Ser374. Its molecular mass measured by mass spectrometry (71,890 +/- 7 Da) is about 30 Da higher than the mass calculated from the sequence data (71,860.1 Da). The origin of this difference is not clear but could result from minor molecular heterogeneities. Within the chelicerates, the Aa6 subunit of the arachnid A. australis shares 405 identical residues with chain e of another arachnid, Eurypelma californicum, and 399 with chain alpha of the merostom Tachypleus tridentatus. The degrees of identity between these three subunits, which are known to occupy the same location in the native hemocyanin oligomers, are significantly higher than those existing between the subunits a, d, and e of E. californicum. This favors the hypothesis that gene duplications, leading to separate chains in one species, have occurred before the divergence between arachnids and merostoms.

Complete amino acid sequence of Proteus mirabilis PR catalase. Occurrence of a methionine sulfone in the close proximity of the active site.

The catalase of Proteus mirabilis PR, a peroxide-resistant (PR) mutant of Proteus mirabilis, binds strongly NADPH, which is a unique property among known bacterial catalases. The enzyme subunit consists of 484 amino acid residues for a mass of 55,647 daltons. The complete amino acid sequence was resolved through the combination of protein sequencing, mass spectrometry, and nucleotide sequencing of a PCR fragment. The sequence obtained was compared with that of other known catalases. Amino acids of the active site are all conserved as well as essential residues involved in NADPH binding. Among the amino acids interacting with the heme, a methionine sulfone was found at position 53, in place of a valine in most other catalases. The origin of oxidation of this methionine is unknown, but the presence of this modification could change iron accessibility by large substrates or inhibitors. This posttranslational modification was also demonstrated in the wild-type P. mirabilis catalase.

Development of a capillary electrophoresis method for the characterization of enzymatic products arising from the carbamoylase digestion of paralytic shellfish poisoning toxins.

A sample stacking procedure is presented for the capillary electrophoretic (CE) separation of paralytic shellfish poisoning (PSP) toxins dissolved in high ionic strength buffers. The application of such a stacking procedure prior to the zone electrophoretic separation is demonstrated for the analysis of decarbamoyl toxins arising from the digestion of PSP toxins by an hydrolytic enzyme from little neck clams (Protothaca staminea). Improvements in separation efficiency facilitated identification and quantitation of substrates and enzymatic products present in the digest using CE. The separation conditions developed were found to be entirely compatible with electrospray mass spectrometry, which permitted the analysis of PSP toxins and their decarbamoyl derivatives present in the low micromolar range in crude enzyme digests. The products released during the enzymatic digestion were identified using CE combined with tandem mass spectrometry.