Methylated lysines and 3-methylhistidine in myosin: tissue and developmental differences

Unique and Novel Urinary Metabolomic Features in Malignant versus Benign Adrenal Neoplasms

Purpose: Adrenal incidentalomas must be differentiated from adrenocortical cancer (ACC). Currently, size, growth, and imaging characteristics determine the potential for malignancy but are imperfect. The aim was to evaluate whether urinary small molecules (<800 Da) are associated with ACC.Experimental Design: Preoperative fasting urine specimens from patients with ACC (n = 19) and benign adrenal tumors (n = 46) were analyzed by unbiased ultraperformance liquid chromatography/mass spectrometry. Creatinine-normalized features were analyzed by Progenesis, SIMCA, and unpaired t test adjusted by FDR. Features with an AUC >0.8 were identified through fragmentation patterns and database searches. All lead features were assessed in an independent set from patients with ACC (n = 11) and benign adrenal tumors (n = 46) and in a subset of tissue samples from patients with ACC (n = 15) and benign adrenal tumors (n = 15) in the training set.Results: Sixty-nine features were discovered and four known metabolites identified. Urinary creatine riboside was elevated 2.1-fold (P = 0.0001) in patients with ACC. L-tryptophan, Nε,Nε,Nε-trimethyl-L-lysine, and 3-methylhistidine were lower 0.33-fold (P < 0.0001), 0.56-fold (P < 0.0001), and 0.33-fold (P = 0.0003) in patients with ACC, respectively. Combined multivariate analysis of the four biomarkers showed an AUC of 0.89 [sensitivity 94.7% (confidence interval {CI}, 73.9%-99.1%), specificity 82.6% (CI, 68.6%-92.2%), PPV 69.2% (CI, 48.2%-85.6%), and NPV 97.4% (CI, 86.5%-99.6%)] for distinguishing ACC from benign tumors. Of the four, creatine riboside and four unknown features were validated. Creatine riboside, Nε,Nε,Nε-trimethyl-L-lysine, and two unknown features were elevated in ACC tumors.Conclusions: There are unique urinary metabolic features in patients with ACC with some metabolites present in patient tumor samples. Urinary creatine riboside can differentiate benign adrenal neoplasms from ACC. Clin Cancer Res; 23(17); 5302-10. ©2017 AACR.

Proteasome mediates removal of proteins oxidized during myocardial ischemia

Numerous proteins are known to be lost following myocardial ischemia/reperfusion yet little is known about the mediating proteinases. This study examines the hypothesis that proteasome plays a significant role in the removal of proteins oxidized during myocardial ischemia. Proteasome was inhibited by perfusing isolated rat hearts with buffer containing lactacystin, 2 micromol/L, for 10 min, which resulted in 51 and 42% decreases in 20S and 26S proteasome activities that persisted for a minimum of 90 min. Lactacystin pretreatment had minor effects on postischemic recovery of isolated hearts exposed to 30 min global ischemia and 60 min reperfusion. Protein carbonyl content of lactacystin-pretreated ischemic hearts was significantly (P < 0.05) increased. One band with approximate molecular mass of 50 kDa is known to contain oxidized actin. Actin degradation was quantitated by analysis of 3-methylhistidine which was significantly (P < 0.05) decreased by 15% following 30 min ischemia and 60 min reperfusion. Pretreatment of ischemic hearts with lactacystin prevented much of the loss (-6.5%) of 3-methylhistidine. Probing immunoprecipitated actin with an antibody specific for ubiquitin revealed no bands containing ubiquitinated homologues of this protein. These observations support the conclusion that proteasome mediates removal of some of the proteins oxidized during myocardial ischemia/reperfusion, and that at least oxidized actin is removed by the 20S proteasome.

The Post-translational Modifications of the Nuclear Encoded Subunits of Complex I from Bovine Heart Mitochondria

Bovine complex I is an assembly of 46 different proteins. Seven of them are encoded in mitochondrial DNA, and the rest are nuclear gene products that are imported into the organelle. Fourteen of the nuclear encoded subunits have modified N termini. Many of these post-translational modifications have been deduced previously from intact protein masses. These assignments have been verified by mass spectrometric analysis of peptides. Thirteen of them are N-alpha-acetylated, and a 14th, subunit B18, is N-alpha-myristoylated. Subunit B18 forms part of the membrane arm of the complex, and the myristoyl group may attach subunit B18 to the membrane. One subunit, B12, has a particularly complex pattern of post-translational modification that has not been analyzed before. It is a mixture of the N-alpha-acetylated form and the form with a free N terminus. In addition, it has one, two, or three methyl groups attached to histidine residues at positions 4, 6, and 8 in various combinations. The predominant form is methylated on residues 4 and 6. There is no evidence for the methylation of histidine 2. Subunit B12 is also part of the membrane arm of complex I, and it probably spans the membrane once, but as its orientation is not known, the methylation sites could be in either the matrix or the intermembrane space. These experiments represent another significant step toward establishing the precise chemical composition of mammalian complex I.

Comparison of the amino acid composition of the intracellular and extracellular matrix protein fractions isolated from avian skeletal muscles

Intracellular and extracellular skeletal muscle protein fractions were isolated from the legs and breasts of young and adult White Leghorn chickens and quantified by detailed amino acid analysis. This involved repeated homogenization in the presence of 50 mM CaCl2, neutral phosphate-buffered saline (pH 7.4), solubilization by 2% sodium dodecyl sulfate (SDS), and centrifugation to separate all intracellular muscle proteins from the extracellular matrix. The total SDS-soluble intracellular muscle proteins in the adult and young birds ranged respectively from 93.2 to 94.5% in the leg and from 93.5 to 94.1% in the breast muscles. Collagen and collagen-like proteins in the extracellular matrix protein fractions were calculated from the amounts of 5-hydroxylysine found in their 96-h acid hydrolysates and elastin content from the amounts of desmosine present. Total collagen ranged from 3.42 to 5.18% in legs and from 2.91 to 3.89% in breasts. The elastin content of leg muscles represents only .061% of the total muscle protein. The calculated protein efficiency ratios for intracellular avian muscle proteins averaged 3.2 compared with a mean value of 1.4 for the extracellular matrix.

Site-directed mutation of the Escherichia coli ada gene: effects of substitution of methyl acceptor cysteine-321 by histidine in Ada protein

Oligodeoxynucleotide-mediated mutagenesis of the ada gene of Escherichia coli was used to produce two mutant Ada proteins. In mutant I the methyl acceptor Cys-321 for O6-methylguanine was replaced by histidine; and in mutant II the positions of Cys-321 and His-322 of the wild-type protein were inverted. Neither mutant protein had O6-methylguanine-DNA methyltransferase activity, but both retained the phosphotriester-DNA methyltransferase activity involving methyl group transfer to Cys-69. Under the control of the endogenous promoter, synthesis of mutant I protein was undetectable before or after adaptation treatment with promoter, synthesis of mutant I protein was undetectable before or after adaptation treatment with N-methyl-N'-nitro-N-nitrosoguanidine. This appeared to be due to both inhibition of transcription of the mutant gene and degradation of the synthesized protein. On the other hand, mutant II protein was inducible by N-methyl-N'-nitro-N-nitrosoguanidine, although to a smaller extent than the wild-type protein was, and the phosphotriester-DNA methyltransferase activity appeared to reside in 24- to 30-kilodalton cleavage products. Mutant I protein could be produced under lac promoter control, and its cleavage products, unlike those of mutant II protein, tended to aggregate. These results indicate that (i) Cys-321 cannot be replaced or transposed with the nucleophilic amino acid histidine for O6-methylguanine-DNA methyltransferase function, (ii) single amino acid replacement or transposition at the O6-methylguanine methyl acceptor site can have a profound effect on the in vivo stability and regulatory function of the Ada protein, and (iii) the integrity of the protein may not be absolutely needed for its transcription-activation function.

Determination of myofibrillar and connective tissue protein contents of young and adult avian (Gallus domesticus) skeletal muscles and the N tau-methylhistidine content of avian actins

The myosin, actin, and collagen contents of young and adult avian red (leg) and white (breast) skeletal muscles from White Leghorn chickens have been determined by the use of analytical chromatographic methods developed to quantify the unique amino acids that occur in these proteins. Because one mole of actin purified from the red and white muscles of Leghorn chickens and one mole of myosin contain respectively one and two moles of N tau-methylhistidine, and the molar ratio of myosin and actin in skeletal muscle is known to be 1:6, the myofibrillar myosin and actin contents of avian skeletal muscles can be determined from the amounts of protein-bound N tau-methylhistidine found in acid hydrolysates of this tissue. Actin accounts for an estimated 11.2 to 12.2% of total muscle mass in both muscles or about 21.1% of total myofibrillar protein, whereas myosin ranges from 23.4 to 25.8% of total protein, corresponding to a mean value of 43.8% of total myofibrillar proteins. Total avian collagen ranged from 1.96 to 3.08% in breast and from 5.63 to 6.87% in leg skeletal muscles. With the methods described herein, content of collagen and collagen-like proteins can be calculated from amounts of 5-hydroxylysine present. The content of total connective tissue proteins could also be calculated from amounts of 4-hydroxyproline found. These quantifications are based on total protein content of the selected avian muscles determined by their detailed amino acid composition.