RimO and MiaB are radical S-adenosylmethionine (SAM) enzymes that catalyze the attachment of methylthio (–SCH3) groups onto macromolecular substrates. RimO attaches a methylthio group at C3 of aspartate 89 of protein S12, a component of the 30S subunit of the bacterial ribosome. MiaB attaches a methylthio group at C2 of N6-(isopentenyl)adenosine, found at nucleotide 37 in several prokaryotic tRNAs. These two enzymes are prototypical members of a subclass of radical SAM (RS) enzymes called methylthiotransferases (MTTases). It had been assumed that the sequence of steps in MTTase reactions involves initial sulfur insertion into the organic substrate followed by capping of the inserted sulfur atom with a SAM-derived methyl group. In this work, however, we show that both RimO and MiaB from Thermotoga maritima (Tm) catalyze methyl transfer from SAM to an acid/base labile acceptor on the protein in the absence of their respective macromolecular substrates. Consistent with the assignment of the acceptor as an iron–sulfur (Fe/S) cluster, denaturation of the SAM-treated protein with acid results in production of methanethiol. When RimO or MiaB is first incubated with SAM in the absence of substrate and reductant, and then incubated with excess S-adenosyl-l-[methyl-d3]methionine ([methyl-d3]-SAM) in the presence of substrate and reductant, production of the unlabeled product precedes production of the deuterated product, showing that the methylated species is chemically and kinetically competent to be an intermediate.

HPLC fractions of diricinoleoylacylglycerols containing one non-ricinoleoyl chain from castor oil were used to identify the regiospecific location of this non-ricinoleoyl chain on the glycerol backbone using electrospray ionization-MS3 of lithium adducts. The regiospecific ions used were from the loss of alpha,beta-unsaturated fatty acid specific at the sn-2 position. The content of 1,3-diricinoleoyl-2-oleoyl-sn-glycerols (ROR) among the three stereospecific isomers, RRO, ROR and ORR, was about 91%. The contents of other 1,3-diricinoleoyl-2-acyl-glycerols among the three stereospecific isomers were as follows: 1,3-diricinoleoyl-2-linoleoyl-sn-glycerol, 95%; 1,3-diricinoleoyl-2-linolenoyl-sn-glycerol, 96%; 1,3-diricinoleoyl-2-stearoyl-sn-glycerol, 96%; 1,3-diricinoleoyl-2-palmitoyl-sn-glycerol, 78%; and 1,3-diricinoleoyl-2-lesqueroloyl-sn-glycerol, 31%. These non-hydroxyl fatty acids were mostly at the sn-2 position of triacylglycerols in castor oil. These results suggest that phospholipase A2 hydrolysis of phosphatidylcholine (PC) containing non-hydroxyl fatty acid at the sn-2 position is either blocked or partially blocked in vivo. Phospholipase A2 hydrolysis of 2-lesqueroloyl-PC is not blocked and is similar to that of 2-ricinoleoyl-PC. Transgenic inhibition of phospholipase C hydrolysis of PC might be used to block the incorporation of non-hydroxyl fatty acids into triacylglycerols, thus increasing the content of ricinoleate in seed oil.

An acylglycerol (AG) containing four acyl chains, (12-ricinoleoylricinoleoyl)diricinoleoylglycerol (RRRR), was positively identified for the first time in a natural source in castor oil using electrospray ionization tandem mass spectrometry (ESI-MS/MS). HPLC-purified RRRR from castor oil was subjected to ion trap and high-resolution ESI-MS/MS. The precursor and fragment ions of [RRRR + Na]+ showed the expected masses, and the sodiated fragment ions of both diacylglycerols and fatty acids were detected. Because fragment ions of fatty acids from [AG + NH4]+ adducts cannot be detected by ESI-MS/MS, [AG + Na]+ adducts are more informative. Radiolabeled triricinolein (RRR) was incorporated into RRRR in castor microsomes, indicating that RRRR is biosynthesized in castor bean. This newly identified and biosynthesized RRRR represents a new AG subclass of tetra-acylglycerols (or acylacyldiacylglycerol).

Cell surface proteins have been shown to be effective therapeutic targets. In addition, shed forms of these proteins and secreted proteins can serve as biomarkers for diseases, including cancer. Thus, identification of cell surface and secreted proteins has been a prime area of interest in the proteomics field. Most cell surface and secreted proteins are known to be glycosylated and therefore, a proteomics strategy targeting these proteins was applied to obtain proteomic profiles from various thyroid cancer cell lines that represent the range of thyroid cancers of follicular cell origin. In this study, we oxidized the carbohydrates of secreted proteins and those on the cell surface with periodate and isolated them via covalent coupling to hydrazide resin. The glycoproteins obtained were identified from tryptic peptides and N-linked glycopeptides released from the hydrazide resin using 2-dimensional liquid chromatography-tandem mass spectrometry in combination with the gas phase fractionation. Thyroid cancer cell lines derived from papillary thyroid cancer (TPC-1), follicular thyroid cancer (FTC-133), Hürthle cell carcinoma (XTC-1), and anaplastic thyroid cancer (ARO and DRO-1) were evaluated. An average of 150 glycoproteins were identified per cell line, of which more than 57 percent are known cell surface or secreted glycoproteins. The usefulness of the approach for identifying thyroid cancer associated biomarkers was validated by the identification of glycoproteins (e.g. CD44, galectin 3 and metalloproteinase inhibitor 1) that have been found to be useful markers for thyroid cancer. In addition to glycoproteins that are commonly expressed by all of the cell lines, we identified others that are only expressed in the more well-differentiated thyroid cancer cell lines (follicular, Hürthle cell and papillary), or by cell lines derived from undifferentiated tumors that are uniformly fatal forms of thyroid cancer (i.e. anaplastic). Based on the results obtained, a set of glycoprotein biomarker candidates for thyroid cancer is proposed.