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PubMed2026

A machine learning-derived intratumoral heterogeneity-related signature predicts the prognosis for and therapeutic response in patients with skin cutaneous melanoma.

BACKGROUND: Reliable biomarkers for predicting prognosis and therapeutic response in skin cutaneous melanoma (SKCM) remain limited. This study aimed to develop an intratumoral heterogeneity (ITH)-related prognostic signature for SKCM using integrative machine learning. METHODS: RNA sequencing (RNA-seq) data from 472 SKCM patients in The Cancer Genome Atlas (TCGA) and 214 patients in the GSE65904 cohort were analyzed. ITH scores were calculated using the DEPTH2 algorithm. Differentially expressed genes (DEGs) were identified between high- and low-ITH groups [|log2fold change (FC)| ≥1, false discovery rate (FDR) <0.05]. Based on 38 prognostic DEGs identified by univariate Cox regression, we employed an integrative framework of 101 machine learning algorithm combinations to construct prognostic models in the TCGA training cohort. The model with the highest average concordance index (C-index) was validated in the GSE65904 cohort and selected as the prognostic ITH-related signature (PIRS). Associations of the PIRS risk score with tumor mutational burden (TMB), immune cell infiltration, immune checkpoint gene expression, and drug sensitivity were systematically evaluated. Model performance was assessed using receiver operating characteristic (ROC) curves and Cox regression analyses. RESULTS: A 38-gene PIRS was constructed using the plsRcox algorithm. Patients with high PIRS risk scores exhibited significantly poorer overall survival (OS) in both the TCGA and Gene Expression Omnibus (GEO) cohorts. The PIRS was identified as an independent prognostic factor, with area under the curve (AUC) values of 0.779, 0.734, and 0.756 for 1-, 3-, and 5-year survival, respectively. High-risk samples displayed significantly lower TMB (P<0.05), reduced immune and stromal cell infiltration (P<0.001), downregulated immune function, and decreased expression of immune checkpoint genes. Additionally, high- and low-PIRS risk score groups exhibited distinct sensitivity patterns to different classes of targeted agents. CONCLUSIONS: The machine learning-derived PIRS robustly predicts prognosis in SKCM patients. Its clinical application is promising for optimizing patient risk stratification and treatment decisions, though further prospective validation is warranted.

Skin cutaneous melanoma (SKCM)↗

PubMed2005

Magnetic resonance imaging signatures of tissue pathology in frontotemporal dementia.

BACKGROUND: The pathologic substrates of frontotemporal dementia (FTD) are difficult to predict in vivo. OBJECTIVE: To determine whether different pathologic substrates of FTD have distinct patterns of regional atrophy on magnetic resonance imaging (MRI). DESIGN: Retrospective case study. SETTING: The Institute of Neurology, University College London, and the Institute of Psychiatry, King's College London. Patients Twenty-one cases of FTD selected on pathologic grounds (9 with ubiquitin-positive [tau- and alpha-synuclein-negative] inclusions [FTD-U], 7 with Pick disease [PiD], and 5 with familial FTD with tau exon 10+16 mutations [tau exon 10+16]) and 20 healthy controls were studied. MAIN OUTCOME MEASURES: Patterns of gray matter atrophy in each group as assessed by voxel-based morphometry (VBM) and a blinded visual assessment of each MRI study. RESULTS: All pathologic substrates were associated with atrophy that involved the inferior and medial temporal and inferior frontal lobes. Additionally, specific VBM signatures were identified for each subgroup: FTD-U was associated with asymmetric (left > right) temporal lobe atrophy, PiD was associated with severe dorsolateral bifrontal atrophy, and tau exon 10+16 was associated with asymmetric (right > left) medial temporal lobe atrophy. The VBM findings were supported by blinded visual assessment. CONCLUSION: These findings suggest that MRI patterns of regional gray matter atrophy constitute signatures of tissue pathology in FTD.

Atrophy↗

PubMed1999

Short-term changes in delta(13)C and delta(15)N signatures of water discharged from grazed grasslands

The composition of dissolved organic matter (DOM) in a soil is the product of a variety of soil processes. Changes in the composition of DOM in water discharged from soil should, therefore, give an important insight into modifications in these soil processes. We hypothesise that these processes in soils, under different grassland management regimes, would be affected to different extents by the short-term disturbance of a storm event and that evidence of this could be detected in delta(13)C and delta(15)N signatures in drainage and surface runoff waters. During a storm event we collected discharge waters from 1 ha grassland lysimeters, with or without artificial drainage, which received contrasting fertiliser inputs, and delta(13)C and delta(15)N signatures were determined. Changes in (13)C enrichment during the storm event were clearly identifiable, as were differences between plots for (13)C and (15)N, illustrating that this technique has potential to be a useful tool for identifying and investigating short- and long-term changes in soil organic matter dynamics. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗

PubMed1999

Dependence of the Raman signature of genomic B-DNA on nucleotide base sequence.

The vibrational spectra of four genomic and two synthetic DNAs, encompassing a wide range in base composition [poly(dA-dT). poly(dA-dT), 0% G + C; Clostridium perfringens DNA, 27% G + C; calf thymus DNA, 42% G + C; Escherichia coli DNA, 50% G + C; Micrococcus luteus DNA, 72% G + C; poly(dG-dC).poly(dG-dC), 100% G + C] (dA: deoxyadenosine; dG: deoxyguanosine; dC: deoxycytidine; dT: thymidine), have been analyzed using Raman difference methods of high sensitivity. The results show that the Raman signature of B DNA depends in detail upon both genomic base composition and sequence. Raman bands assigned to vibrational modes of the deoxyribose-phosphate backbone are among the most sensitive to base sequence, indicating that within the B family of conformations major differences occur in the backbone geometry of AT- and GC-rich domains. Raman bands assigned to in-plane vibrations of the purine and pyrimidine bases-particularly of A and T-exhibit large deviations from the patterns expected for random base distributions, establishing that Raman hypochromic effects in genomic DNA are also highly sequence dependent. The present study provides a basis for future use of Raman spectroscopy to analyze sequence-specific DNA-ligand interactions. The demonstration of sequence dependency in the Raman spectrum of genomic B DNA also implies the capability to distinguish genomic DNAs by means of their characteristic Raman signatures.

Animals↗

PubMed2001

Analysis of sequence signature defining functional specificity and structural stability in helix-loop-helix proteins.

Specific functional properties of many proteins directing developmental responses via transcriptional regulation are orchestrated by their characteristic helix-loop-helix (HLH) structural motif. The entire HLH motif in all these proteins assumes a common conformation irrespective of their individual biological effects. The motif controls the affinity of HLH proteins for homo- or heterodimerization, permitting mixing and matching of regulatory factors, and thereby expanding the functional repertoire. Systematic analysis of molecular contacts at the dimer interface using the models built for the functional dimers combined with the pattern of conserved/nonconserved residues within different categories of HLH proteins helped in understanding the differential role played by different residues at the dimer interface for expressing corresponding functions. The residues associated with the self and partner interactions were identified, and the signature residues contributing toward dimeric stability and functional specificity were defined. It is evident that most of the residues involved in self interactions are common among all the HLH proteins. However, while certain residues involved in partner interactions are common among all the HLH proteins, certain others are common within a category, and still others vary widely defining specificity signature at different levels.

Amino Acid Sequence↗

PubMed2006

Individual olfactory signatures in common marmosets (Callithrix jacchus).

Individual discrimination is likely a prerequisite for most primate social interactions. Olfactory cues are one set of stimuli used by primates to discriminate between individuals. Despite the importance of these olfactory signatures, there is little published research assessing the existence or function of individually unique odors among primates. This review systematically assesses behavioral and biochemical aspects of individual odors in a New World primate, the common marmoset (Callithrix jacchus). There are three objectives to this review: First, behavioral evidence for odors unique to the individual is evaluated in the context of results demonstrating that marmosets are able to discriminate between the scents from a familiar and a novel individual conspecific in behavioral bioassays under a variety of conditions. Second, biochemical evidence for individual scent signatures is debated with reference to studies examining qualitative and quantitative differences between the chemical compositions of scent-mark pools from adult females. A combined gas chromatography (GC) and mass spectrometry (MS) analysis demonstrated that each female had a unique ratio of highly volatile chemicals in the scent mark that could affect individual discrimination. Finally, the possible adaptive significance of individual odors in marmosets is debated. Individual odors may play a key role in regulating both female intrasexual competition and intersexual communication by providing a basis for the assessment of individual quality.

Adaptation, Physiological↗

PubMed2002

Temperature dependence of the Raman spectrum of DNA. II. Raman signatures of premelting and melting transitions of poly(dA).poly(dT) and comparison with poly(dA-dT).poly(dA-dT).

The temperature dependence of the Raman spectrum of poly(dA).poly(dT) (dA: deoxyadenosine; dT: thymidine), a model for DNA containing consecutive adenine.thymine (A.T) pairs, has been analyzed using a spectrometer of high spectral precision and sensitivity. Three temperature intervals are distinguished: (a) premelting (10 < t < 70 degrees C), in which the native double helix is structurally altered but not dissociated into single strands; (b) melting (70 < t < 80 degrees C), in which the duplex is dissociated into single strands; and (c) postmelting (80 < t degrees C), in which no significant structural change can be detected. The distinctive Raman difference signatures observed between 10 and 70 degrees C and between 70 and 80 degrees C are interpreted in terms of the structural changes specific to premelting and melting transitions, respectively. Premelting alters the low-temperature conformation of the deoxyribose-phosphate backbone and eliminates base hydrogen bonding that is distinct from canonical Watson-Crick hydrogen bonding; these premelting perturbations occur without disruption of base stacking. Conversely, melting eliminates canonical Watson-Crick pairing and base stacking. The results are compared with those reported previously on poly(dA-dT).poly(dA-dT), the DNA structure consisting of alternating A.T and T.A pairs (L. Movileanu, J. M. Benevides, and G. J. Thomas, Jr. Journal of Raman Spectroscopy, 1999, Vol. 30, pp. 637-649). Poly(dA).poly(dT) and poly(dA-dT).poly(dA-dT) exhibit strikingly dissimilar temperature-dependent Raman profiles prior to the onset of melting. However, the two duplexes exhibit very similar melting transitions, including the same Raman indicators of ruptured Watson-Crick pairing, base unstacking and collapse of backbone order. A detailed analysis of the data provides a comprehensive Raman assignment scheme for adenosine and thymidine residues of B-DNA, delineates Raman markers diagnostic of consecutive A.T and alternating A.T/T.A tracts of DNA, and identifies the distinct Raman difference signatures for premelting and melting transitions in the two types of sequences.

Base Composition↗

PubMed2001

Raman signatures of ligand binding and allosteric conformation change in hexameric insulin.

Hexameric insulin is an allosteric protein that undergoes transitions between three conformational states (T(6), T(3)R(3), and R(6)). These allosteric states are stabilized by the binding of ligands to the phenolic pockets and by the coordination of anions to the His B10 metal sites. Raman difference (RD) spectroscopy is utilized to examine the binding of phenolic ligands and the binding of thiocyanate, p-aminobenzoic acid (PABA), or 4-hydroxy-3-nitrobenzoic acid (4H3N) to the allosteric sites of T(3)R(3) and R(6). The RD spectroscopic studies show changes in the amide I and III bands for the transition of residues B1-B8 from a meandering coil to an alpha helix in the T-R transitions and identify the Raman signatures of the structural differences among the T(6), T(3)R(3), and R(6) states. Evidence of the altered environment caused by the approximately 30 A displacement of phenylalanine (Phe) B1 is clearly seen from changes in the Raman bands of the Phe ring. Raman signatures arising from the coordination of PABA or 4H3N to the histidine (His) B10 Zn(II) sites show these carboxylates give distorted, asymmetric coordination to Zn(II). The RD spectra also reveal the importance of the position and the type of substituents for designing aromatic carboxylates with high affinity for the His B10 metal site.

Allosteric Site↗

PubMed2006

Utility of molecular genetic signatures in the delineation of gastric neoplasia.

BACKGROUND: Current techniques to define gastric neoplasia are limited but molecular genetic signatures can categorize tumors and provide biological rationale for predicting clinical behavior. We identified three gene signatures: Chromogranin A (CgA), MAGE-D2 (adhesion), and MTA1 (metastasis) that define gastrointestinal (GI) carcinoids and hypothesize that their expression can delineate gastric neoplasia. This strategy provides a molecular basis to define neuroendocrine gastric carcinoids (GCs), neuronal stromal tumors (GISTs), or epithelial cell (gastric adenocarcinomas [GCAs])-derived tumors. METHODS: Total RNA was isolated from 38 GCs: Type I/II (n = 7), Type III/IV (n = 6), GISTs (n = 12), GCAs (n = 13), and normal mucosa (n = 12). Quantitative reverse transcriptase polymerase chain reaction (Q RT-PCR) gene expression was quantified against glyseraldehyde-3-phosphate dehydrogenase (GAPDH) and CgA and MTA1 protein expression levels were analyzed by immunohistochemical analyses of a gastric neoplasia microarray. RESULTS: CgA was elevated in Type I/II (10-fold; P < .01) and Type III/IV (100-fold, P < .005), decreased in GISTs (100-fold, P < .03), and unchanged in GCAs. MAGE-D2 was 5-10-fold elevated (P < .05) in Type III/IV, GISTs, and GCAs but not in Type I/II tumors. MTA1 (> 5-fold, P < .01) was elevated in GCs (Type III/IV>I/II, P < .05), in GISTs (> 4-fold, P < .05), and GCAs. CgA protein levels were elevated in GCs (P < .005) but not in GISTs and GCAs. MTA1 levels were elevated in all tumors (P < .02) compared with normal, and especially with tumor invasion (P < .05). CONCLUSION: CgA discriminates GCs from other gastric neoplasms; overexpression of MAGE-D2 and MTA1 differentiate Type III/IV from Type I/II GCs. GISTs share similar expression patterns with Type III/IV GCs but have decreased CgA. MTA1 is a marker of tumor invasion.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Class distinction between follicular adenomas and follicular carcinomas of the thyroid gland on the basis of their signature expression.

BACKGROUND: Nodules of the thyroid gland are observed frequently in patients who undergo ultrasound studies. The majority of these nodules are benign, corresponding to goiters or adenomas, and only a small fraction corresponds to carcinomas. Among thyroid tumors, the diagnosis of follicular adenocarcinomas by preoperative fine-needle aspiration biopsy is a major challenge, because it requires inspection of the entire capsule to differentiate it from adenoma. Consequently, large numbers of patients undergo unnecessary thyroidectomy. METHODS: Using data from gene expression analysis, the authors applied Fisher linear discriminant analysis and searched for expression signatures of individual samples of adenomas and follicular carcinomas that could be used as molecular classifiers for the precise classification of malignant and nonmalignant lesions. RESULTS: Fourteen trios of genes were described that fulfilled the criteria for the correct classification of 100% of samples. The robustness of these trios was verified by using leave-1-out cross-validation and bootstrap analyses. The results demonstrated that, by combining trios, better classifiers could be generated that correctly classified >92% of samples. CONCLUSIONS: The strategy of classifiers based on individual signatures was a useful strategy for distinguishing between samples with very similar expression profiles.

Adenocarcinoma, Follicular↗

PubMed2026

Dietary Polyphenol Acteoside-Related Molecular Signatures in Clear Cell Renal Cell Carcinoma: Multi-Omics Profiling and Functional Validation of IMPDH1.

Clear cell renal cell carcinoma (ccRCC) is characterized by substantial metabolic and molecular heterogeneity, but the disease-relevant programs associated with acteoside, a dietary polyphenol, remain poorly understood. We integrated predicted acteoside targets with bulk, single-cell, and spatial transcriptomic data from ccRCC and combined molecular subtyping with cross-cohort machine-learning analysis. Acteoside-related signatures were preferentially enriched in malignant compartments and increased with tumor grade and stage. Consensus clustering identified two molecular subtypes with distinct biological and clinical features. C1 was associated with immune activation, metabolic activity, and more favorable survival, whereas C2 showed greater genomic instability, reduced renal epithelial differentiation, and poorer outcomes. We further benchmarked multiple machine-learning strategies and established a 10-gene prognostic model that retained predictive performance across independent cohorts, with IMPDH1 emerging as the strongest risk-associated feature. Functional experiments confirmed the biological relevance of IMPDH1: its knockdown suppressed ccRCC cell proliferation, DNA synthesis, colony formation, and migration, whereas overexpression produced the opposite effects. Together, these findings indicate that acteoside-related molecular signatures capture clinically relevant heterogeneity in ccRCC and provide a framework for linking dietary-polyphenol-related molecular space with tumor biology. The identification and functional validation of IMPDH1 further highlight its potential importance in ccRCC progression.

IMPDH1↗

PubMed2006

Molecular signatures of soy-derived phytochemicals in androgen-responsive prostate cancer cells: a comparison study using DNA microarray.

The present study utilized microarray technology as a tool to elucidate the molecular signatures of soy-derived phytochemicals in the human androgen-responsive prostate cancer cell line LNCaP. Global gene expression pattern analysis of LNCaP cells exposed to 0, 1, 5, or 25 microM of the soy-derived phytochemicals equol and daidzein were conducted and compared. The data were further compared with previously generated data from exposure of LNCaP cells to the same doses of genistein, a soy isoflavone. Multidimensional scaling (MDS) analyses of the expression patterns suggest that these compounds exerted differential effects on gene expression in LNCaP cells. Further examination of specific gene changes revealed that these compounds differentially modulated genes in multiple cellular pathways, including the cell-cycle pathway genes. However, the three compounds also exerted similar effect on genes belonging to several other important cellular pathways. A universal effect of the three compounds on androgen-responsive genes, IGF-1 pathway gene, and MAP kinase-related pathway gene was observed. These results provide the foundation for establishing molecular signatures for equol, daidzein, and genistein. Moreover, these results also allow for the identification of candidate mechanism(s) by which soy phytochemicals and soy may act in prostate cancer cells.

Androgens↗

PubMed2005

Distinct temporal genetic signatures of neurogenic and gliogenic cues in cortical stem cell cultures.

Cortical progenitor cells from rat embryos give rise to neurons or glia following exposure to platelet derived growth factor (PDGF) or ciliary neurotrophic factor (CNTF), respectively. Both growth factors impart their developmental cues quickly through a transcription-dependent mechanism. Do the alternate developmental responses to PDGF and CNTF reflect induction of qualitatively distinct genes? Alternatively, do the same genes respond to each growth factor, but with quantitatively distinct kinetics? Using differential library screening and custom cDNA microarrays we show that a common set of genes responds to either growth factor. However, quantitative differences in the onset and duration of gene induction equate to the expression of factor-specific gene signatures. Multitissue cluster analysis also reveals tissue-specific gene signatures that may play important roles in the developing brain.

Animals↗

PubMed2004

Immunophenotypic analysis of inflammatory breast cancers: identification of an 'inflammatory signature'.

Inflammatory breast cancer (IBC) is a rare but very aggressive form of breast cancer. Its definition is based on clinical criteria, but a molecular definition could be useful when data are incomplete or features are missing. Recently, the identification of overexpression of E-cadherin in IBC has improved understanding of the molecular basis of this disease. Consequently, the aim of this study was to try to determine an immunophenotypic 'signature' of IBC. A series of 80 cases of IBC were compared with 552 non-IBC control cases and a model was elaborated to evaluate the probability of an inflammatory carcinoma being present in any clinical situation. Tissue microarrays (TMAs) were used to determine the immunohistochemical profile of eight proteins including E-cadherin, EGFR, oestrogen and progesterone receptor (ER and PR), MIB1, ERBB2, MUC1, and P53. All the parameters tested were differentially expressed between IBC and control cases in univariate analysis (p < 0.001). The five variables that were significantly associated with IBC in multivariate analysis were E-cadherin > or = 300 [HR = 5.64 (2.92-10.87)], ER negative [HR = 3.00 (1.67-5.51)], MIB1 > 20 [HR = 3.54 (1.87-6.71)], MUC1 cytoplasmic staining [HR = 2.72 (1.49-4.96)], and ERBB2 positive 2+ or 3+ [HR = 2.46 (1.26-4.78)]. The probability that a breast cancer with this full phenotype at diagnosis was an IBC was 90.5%. If any one of the five parameters was missing, this probability dropped to 75% and was less than 50% when one, two, or three parameters were present. The 5-year overall survival (OS) and 5-year disease-free survival (DFS) of patients with IBC were not significantly different from those of the non-IBC control group that expressed four or five parameters (nIBC-1), but this nIBC-1 control group had a significantly worse outcome than the non-IBC control group (nIBC-2) with only 0-3 parameters (p = 0.0049 for OS and p < 0.0001 for DFS). In conclusion, an immunophenotypic signature was suggested for IBC. This could help to determine the worst cases, independent of clinical criteria.

Adult↗

PubMed2006

Proteome signatures for stress and starvation in Bacillus subtilis as revealed by a 2-D gel image color coding approach.

In this paper we have defined proteome signatures of Bacillus subtilis in response to heat, salt, peroxide, and superoxide stress as well as after starvation for ammonium, tryptophan, glucose, and phosphate using the 2-D gel-based approach. In total, 79 stress-induced and 155 starvation-induced marker proteins were identified including 50% that are not expressed in the vegetative proteome. Fused proteome maps and a color coding approach have been used to define stress-specific regulons that are involved in specific adaptative functions (HrcA for heat, PerR and Fur for oxidative stress, RecA for peroxide, CymR and S-box for superoxide stress). In addition, starvation-specific regulons are defined that are involved in the uptake or utilization of alternative nutrient sources (TnrA, sigmaL/BkdR for ammonium; tryptophan-activated RNA-binding attenuation protein for tryptophan; CcpA, CcpN, sigmaL/AcoR for glucose; PhoPR for phosphate starvation). The general stress or starvation proteome signatures include the CtsR, Spx, sigmaL/RocR, sigmaB, sigmaH, CodY, sigmaF, and sigmaE regulons. Among these, the Spx-dependent oxidase NfrA was induced by all stress conditions indicating stress-induced protein damages. Finally, a subset of sigmaH-dependent proteins (sporulation response regulator, YvyD, YtxH, YisK, YuxI, YpiB) and the CodY-dependent aspartyl phosphatase RapA were defined as general starvation proteins that indicate the transition to stationary phase caused by starvation.

Bacillus subtilis↗

PubMed1992

Amino acid binding by the class I aminoacyl-tRNA synthetases: role for a conserved proline in the signature sequence.

Although partial or complete three-dimensional structures are known for three Class I aminoacyl-tRNA synthetases, the amino acid-binding sites in these proteins remain poorly characterized. To explore the methionine binding site of Escherichia coli methionyl-tRNA synthetase, we chose to study a specific, randomly generated methionine auxotroph that contains a mutant methionyl-tRNA synthetase whose defect is manifested in an elevated Km for methionine (Barker, D.G., Ebel, J.-P., Jakes, R.C., & Bruton, C.J., 1982, Eur. J. Biochem. 127, 449-457), and employed the polymerase chain reaction to sequence this mutant synthetase directly. We identified a Pro 14 to Ser replacement (P14S), which accounts for a greater than 300-fold elevation in Km for methionine and has little effect on either the Km for ATP or the kcat of the amino acid activation reaction. This mutation destabilizes the protein in vivo, which may partly account for the observed auxotrophy. The altered proline is found in the "signature sequence" of the Class I synthetases and is conserved. This sequence motif is 1 of 2 found in the 10 Class I aminoacyl-tRNA synthetases and, in the known structures, it is in the nucleotide-binding fold as part of a loop between the end of a beta-strand and the start of an alpha-helix. The phenotype of the mutant and the stability and affinity for methionine of the wild-type and mutant enzymes are influenced by the amino acid that is 25 residues beyond the C-terminus of the signature sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed2006

Are structural biases at protein termini a signature of vectorial folding?

Experimental investigations of the biosynthesis of a number of proteins have pointed out that part of the native structure may be acquired already during translation. We carried out a comprehensive statistical analysis of some average structural properties of proteins that have been put forward as possible signatures of this progressive buildup process. Contrary to a widespread belief, we found that there is no major propensity of the amino acids to form contacts with residues that are closer to the N-terminus. Moreover, we found that the C-terminus is significantly more compact and locally organized than the N-terminus. This bias, though, is unlikely to be related to vectorial effects, since it correlates with subtle differences in the primary sequence. These findings indicate that even if proteins acquire their structure vectorially, no signature of this seems to be detectable in their average structural properties.

Databases, Protein↗

PubMed2005

Mass spectral signature for insect adipokinetic hormones.

Insect adipokinetic hormones (AKHs) are structurally similar. They consist of 8 to 10 amino acid residues, and are post-translationally modified at the N-terminus (pyroglutamic acid) and at the C-terminus (carboxyamide). They contain aromatic amino acids at position 4 (mostly Phe, in a few cases Tyr) and at position 8 (Trp). Position 9 is always Gly which is used in the octapeptides for the amidation, and the majority of the peptides have no charge. AKHs exhibit a characteristic ion signature both in matrix-assisted laser desorption/ionization (ion pair [M+Na](+)/[M+K]+) and in electrospray mass spectrometry ([M+H+K]2+, [M-17+H]+, [M+H]+, [M+Na]+, [M+K]+). Their high affinity for Na+ and K+ alkali cations is observed even after reversed-phase purification. AKHs rarely form doubly charged ions with protons or sodium while the [M+H+K]2+ ion is often abundant suggesting a special conformation of the larger metal ion complex possibly related to its size. Here, we present analyses of several AKHs of different insect species and discuss their ionization behavior with respect to their sequence. The mass spectral signature observed is useful for AKH detection from mixtures and so an unassigned 990.7 Da molecule was found in dragonfly which is currently under investigation.

Amino Acid Sequence↗