Identification of peptides containing tryptophan, tyrosine, and phenylalanine using photodiode-array spectrophotometry

A Diphenylalanine Based Pentapeptide with Fibrillating Self-Assembling Properties

Peptides and their related compounds can self-assemble into diverse nanostructures of different shapes and sizes in response to various stimuli such as pH, temperature or ionic strength. Here we report the synthesis and characterization of a lysozyme derived pentapeptide and its ability to build well-defined fibrillar structures. Lysozyme FESNF peptide fragment was synthesized by solid phase peptide synthesis using the Fmoc/t-Bu strategy, purified by analytical high-performance liquid chromatography (HPLC) and its molecular weight was confirmed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Spectroscopic features of this pentapeptide were investigated by UV-visible spectroscopy and fluorimetry showing the pattern of marginal phenylalanine residues within the peptide sequence. Self-assembling properties were determined using atomic force microscopy (AFM), aggregation index and thioflavin T assay (ThT). FESNF generating fibrillar structures observed by AFM and aggregation propensity were primarily influenced by pH conditions. Moreover, the experimental data were confirmed by molecular dynamics simulation studies. The obtained fibrils will be used next to explore their potential to act as support material for medical and cosmetic application.

Variation of protein corona composition of gold nanoparticles following plasmonic heating

It is well recognized that the primary interaction of most biological environments with nanoparticles (NPs) is strongly influenced by a long-lived ("hard") protein corona that surrounds the NP and remains strongly adsorbed to its surface. The amount and composition of associated proteins in the corona adsorbed onto the NPs is related to several important factors, including the physicochemical properties of the NPs and the composition of the protein solution. Here, for the first time, it is shown that plasmonic heat induction (by laser activation) leads to significant changes in the composition of the hard protein corona adsorbed on low aspect ratio gold nanorods. Using mass spectrometry, several proteins in the corona were identified whose concentrations change most substantially as a result of photoinduced (plasmonic) heating versus simple thermal heating. Molecular modeling suggests that the origin of these changes in protein adsorption may be the result of protein conformational changes in response to much higher local temperatures that occur near the gold nanorods during photoinduced, plasmonic heating. These results may define new applications in vivo for NPs with hyperthermia capability and better define the likely interactions of cells with NPs after plasmonic heating. Potential changes in the protein corona following hyperthermia treatment may influence the final biological fate of plasmonic NPs in clinical applications and help elucidate safety considerations for hyperthermia applications.

Bradykinin degradation pathways in human blood plasma

The kinetics of proteolysis of bradykinin and its metabolites in human blood plasma was studied, the limiting stages were determined and each stage of the degradation was correlated with the appropriate plasma enzyme. A scheme of the pathways of major and minor degradation processes has been proposed.

Protein estimation by the product of integrated peak area and flow rate

A convenient method for protein estimation is described, making use of uv detectors and peak integrators that are standard equipment on modern high-performance liquid chromatographs to determine the product of integrated peak area and flow rate of eluting protein at 214 nm (AF214). We demonstrate that AF214 is proportional to the amount of eluted protein and describe two approaches for calibrating the integrator, by quantitative amino acid analysis and by determining the elution yield of a known amount of applied protein, allowing direct estimation of protein from AF214. Both approaches yield similar results. The basis for the method is that, for virtually all proteins, absorbance at 214 nm is dominated by the summed contributions from the peptide groups. More accurate estimates can be made when the amino acid composition of the eluting protein is known, since this permits a correction to be made for contributions of amino acid side chains to absorbance at 214 nm. Comparison of AF214 estimates for proteins from the small (30 S) subunit of the Escherichia coli ribosome with those obtained by Bradford analysis shows the latter to give somewhat higher values.

High-performance liquid chromatographic determination of substance P-like arginine-containing peptide in rat brain by on-line post-column fluorescence derivatization with benzoin

A high-performance liquid chromatographic method with fluorescence detection is described for the determination of substance P, one of the neuropeptides, in the hypothalamus tissue of rat brain. The detection is based on on-line post-column fluorescence derivatization selective for arginine-containing peptides. The endogenous substance P-like arginine-containing peptide extracted from the tissue and [D-Phe11]-neurotensin as an internal standard were separated from various interfering substances on a reversed-phase column (TSKgel ODS-120T) by gradient elution with acetonitrile-phosphate buffer (pH 2.3). The peptides in the eluate were then automatically converted into fluorescent derivatives for detection by reaction with benzoin. Arginine-containing fragments produced by the enzyme reaction of substance P in the chromatographic fraction with trypsin were also detected, for the identification of the endogenous substance P-like arginine-containing peptide. The method was sensitive enough to permit the quantitative determination of the peptide at a concentration as low as 580 fmol/mg of protein in the brain homogenate. The concentration values of the substance P-like arginine-containing peptide in the tissue were 9.45 +/- 1.50 pmol/mg of protein (six determinations).

On-line post-column fluorescence derivatization of arginine-containing peptides in high-performance liquid chromatography

A selective detection system based on on-line post-column fluorescence derivatization is described for the analysis of arginine-containing peptides by high-performance liquid chromatography. The peptides are automatically converted into fluorescent derivatives with benzoin, a fluorogenic reagent for guanidino compounds, after separation on a reversed-phase column (TSKgel ODS-120T) and detection in an ultraviolet absorption detector. The system permits fluorescence detection at 435 nm emission with irradiation at 325 nm for arginine-containing peptides in as little as picomole amounts. The chromatogram obtained with fluorescence detection only shows peaks corresponding to arginine-containing peptides. The facile detection of arginine-containing fragments in the tryptic digest of beta-melanocyte stimulating hormone as a model compound could be achieved by comparison with a chromatogram obtained with ultraviolet absorption detection at 215 nm.

Determination of the molecular mass of apolipoprotein B-100. A chemical approach

Apolipoprotein B-100 (apo B-100) is the protein ligand in low-density lipoproteins that binds to a specific cell-surface receptor. Its molecular mass has been a subject of controversy. We have determined the molecular mass of the protein by a chemical approach. After complete CNBr cleavage, the C-terminal fragment of apo B-100 was purified by reverse-phase h.p.l.c. Amino acid N- and C-terminal analyses confirm that this peptide represents the C-terminal peptide as deduced from the DNA sequence of a human apo B-100 cDNA clone. A chemically synthesized peptide was used to determine the recovery of the peptide (74.72%). On the basis of these data, the molecular mass of apo B-100 was determined to be 496.82 +/- 24.84 kDa.

The primary structure of apolipoprotein A-I from rabbit high-density lipoprotein

The amino acid sequence of rabbit apolipoprotein A-I (apo A-I) has been determined by degradation and alignment of two overlapping sets of peptides obtained from tryptic and staphylococcal digestions. All of the peptides of rabbit apo A-I resulting from digestion by staphylococcal protease were isolated and sequenced except residues 33-37. A digestion with trypsin was employed to find overlapping and missing peptides. The N-terminus of rabbit apo A-I was confirmed by sequencing the intact protein up to 20 residues while the C-terminus was identified through its homology with human apo A-I. The protein contains 241 residues in its single chain. Its primary structure is highly homologous to the reported canine apo A-I (80%) and human apo A-I (78%), but exhibits less similarity with rat apo A-I (60%). Like human apo A-I, rabbit apo A-I contains very little histidine (2) and methionine (1); it does however have two residues of isoleucine. Based on a comparison of the hydrophobic-hydrophilic character of apo A-I residues with that of the two synthetic peptides that activated lecithin: cholesterol acyltransferase (Pownall et al. and Yokoyama et al.), we found that the five segments with the highest corresponding homologies on the protein are located within the N-terminal half. This suggests that the N-terminal half of apo A-I contains the major portion of regions activating lecithin: cholesterol acyltransferase.

High-performance liquid chromatography and diode-array detection for the identification of peptides containing aromatic amino acids in studies of endorphin-degrading activity in human cerebrospinal fluid

Diode-array UV detection has been adapted for analysis of opioid peptides and their metabolic fragments differing in aromatic amino acid content. In combination with high-performance liquid chromatography, the technique allowed a direct and rapid discrimination between peptides containing phenylalanine, tryptophan and tyrosine, or a combination of these residues. Enkephalin fragments with either tyrosine or phenylalanine, or both, were identified after digestion of the pentapeptide with proteolytic activity recovered from human cerebrospinal fluid. The N-terminal tyrosine-containing fragment of dynorphin A was identified after hydrolysis of the peptide by a cerebrospinal fluid endopeptidase. The study was extended to the analysis of some non-opioid peptides. The Tyr1 analogue of delta-sleep-inducing peptide was easily distinguished from the authentic compound with a tryptophan at the N-terminus. Results indicated that the technique was useful for discriminating between dipeptides differing in aromatic residues that were unresolved by high-performance liquid chromatography.

Molecular cloning and expression of partial cDNAs and deduced amino acid sequence of a carboxyl-terminal fragment of human apolipoprotein B-100

Apolipoprotein (apo) B-100 cDNAs were identified in a human liver cDNA library cloned in the expression vector lambda gt11. The beta-galactosidase-apoB-100 fusion protein was detected by two independently produced low density lipoprotein polyclonal antisera and by three apoB-100 monoclonal antibodies that crossreact with apoB-74. It was not recognized by two apoB-100 monoclonal antibodies that crossreact with apoB-26. The longest clone, lambda B8, was completely sequenced. It contains a 2.8-kilobase DNA fragment containing the codons for the carboxyl-terminal 836 amino acid residues of apo-B-100, as well as the 3' untranslated region of apoB-100 mRNA. We have thus mapped apoB-74 to the carboxyl-terminal portion of apoB-100. The deduced amino acid sequence of the cloned DNA matches the sequences of 14 apoB-100 peptides determined in our laboratory. Minor differences in amino acid sequence were noted in three of the peptides, suggesting polymorphism of apoB-100 at the protein and DNA levels. Secondary structure predictions reveal an unusual pattern for apolipoproteins, consisting of beta-structure (24%), alpha-helical content (33%), and random structure (30%). Ten amphipathic helical regions of 10-24 residues were identified. This carboxyl-terminal fragment of apoB-100 is considerably more hydrophobic than other apolipoproteins with known structure. Its lipid binding regions might include stretches of highly hydrophobic beta-sheets as well as amphipathic helices. Our findings on apoB structure might be important for understanding the role of apoB-100-containing lipoproteins in atherosclerosis.

Isolation and primary structure determination of amphibian skin tryptophyllins

A large new set of peptides has been isolated from the skin of Phyllomedusa rohdei, a South American frog. All these peptides contain a tryptophyl residue, which justified the suggested denomination of tryptophyllins (TPHs). On the basis of their amino acid chain length, they have been classified as TPH-4, TPH-5, TPH-7 and TPH-13. With the exception of TPH-13 these peptides seem to possess an action on liver protein synthesis and body weight; in addition TPH-7 and TPH-13 show endocrine and behavioural effects. The methodologies employed in purification and structure determination of TPHs will be illustrated.