Peptide design based on an antibody complementarity-determining region (CDR): construction of porphyrin-binding peptides and their affinity maturation by a combinatorial method

We have utilized sequence information from an antiheme monoclonal antibody to develop novel porphyrin-binding peptides. Several peptides which have an intramolecular disulfide bond in different positions and different chain lengths were prepared. The affinities of peptides for meso-tetrakis(4-carboxyphenyl)porphyrin were increased by an appropriate conformational restraint using a disulfide bond. Detailed studies with a representative 12-peptide, 12C4, whose length was reduced from 20 residues of the complementarity-determining region (CDR), indicated that both the hydrophobic and electrostatic interactions were essential factors in the peptide-porphyrin binding. Moreover, two-dimensional 1H NMR spectroscopy revealed the conformation of the peptide and the critical residues for the porphyrin-binding. According to the obtained results, a further minimized 9-peptide, 9L, was successfully redesigned with a sequence capable of forming a beta-turn instead of a disulfide bond. Furthermore, affinity maturation studies of 9L were performed by using a combinatorial approach such as the spot-synthesis method. Peptides with an improved affinity for porphyrins were prepared by systematic amino acid replacement. Thus, the design of peptides targeted to porphyrins was demonstrated by the combination of antibody information and the rationally designed combinatorial method.

A high-throughput screening utilizing intramolecular fluorescence resonance energy transfer for the discovery of the molecules that bind HIV-1 TAR RNA specifically

A 16-residue peptide, including the Tat(49-57) sequence was labeled with a fluorescein and a tetramethylrhodamine at its N- and C-terminus, respectively. This double dye-labeled peptide was prepared as a tracer for high-throughput screening utilizing intramolecular fluorescence resonance energy transfer (FRET). The binding of the competitor molecules for HIV-1 TAR RNA were monitored and dissociation constants of those molecule were determined by using this tracer. This novel screening system might be useful to discover the drug for HIV-1 TAR RNA.

Escherichia coli NifS-like proteins provide selenium in the pathway for the biosynthesis of selenophosphate

Selenophosphate synthetase (SPS), the selD gene product from Escherichia coli, catalyzes the biosynthesis of monoselenophosphate, AMP, and orthophosphate in a 1:1:1 ratio from selenide and ATP. Kinetic characterization revealed the K(m) value for selenide approached levels that are toxic to the cell. Our previous demonstration that a Se(0)-generating system consisting of l-selenocysteine and the Azotobacter vinelandii NifS protein can replace selenide for selenophosphate biosynthesis in vitro suggested a mechanism whereby cells can overcome selenide toxicity. Recently, three E. coli NifS-like proteins, CsdB, CSD, and IscS, have been overexpressed and characterized. All three enzymes act on selenocysteine and cysteine to produce Se(0) and S(0), respectively. In the present study, we demonstrate the ability of each E. coli NifS-like protein to function as a selenium delivery protein for the in vitro biosynthesis of selenophosphate by E. coli wild-type SPS. Significantly, the SPS (C17S) mutant, which is inactive in the standard in vitro assay with selenide as substrate, was found to exhibit detectable activity in the presence of CsdB, CSD, or IscS and l-selenocysteine. Taken together the ability of the NifS-like proteins to generate a selenium substrate for SPS and the activation of the SPS (C17S) mutant suggest a selenium delivery function for the proteins in vivo.

Design of artificial pepetides that recognize the HIV RRE IIB RNA

Peptide nucleic acid (PNA) conjugated peptides, derived from HIV-1 Rev, were designed and synthesized in order to construct molecules that recognize HIV RRE IIB RNA. The competitive binding analyses using fluorescent Rev peptide revealed that the PNA unit on the peptide affected the RNA binding.

Design of peptides undergoing self-catalytic alpha-to-beta transition and amyloidogenesis

Improved understanding of amyloidogenic peptides and proteins such as prion proteins and Alzheimer's beta peptides has attracted much attention to the elucidation of the molecular mechanisms of such amyloidogenesis. As a representative, in the prion protein, the conformational transitions from alpha-helix to beta-structure undergo along with the amyloidogenesis in a self-catalytic manner. Moreover, recent studies by the de novo design of peptides and proteins as well as the amyloidogenesis of peptides and proteins including pathogenic protein mutants have provided insight into the conformational changes essential to amyloidogenesis and correct folding.

Degradation of human Aurora2 protein kinase by the anaphase-promoting complex-ubiquitin-proteasome pathway

Human Aurora2 was originally identified by its close homology to yeast IPL1 and fly aurora, which are key regulators of chromosome segregation and a family of serine/threonine kinases. Here we demonstrate that the Aurora2 protein is degraded rapidly after G2/M phase release in mammalian cells. Aurora2 protein has a rapid turnover rate with a half-life of approximately 2 h. In eukaryotic cells, the ubiquitin-proteasome pathway is the major mechanism for the targeted degradation of unstable proteins. The treatment of mammalian cells with proteasome inhibitors blocks Aurora2 degradation. Furthermore, Aurora2 is polyubiquitinated in vivo and in vitro using anaphase-promoting complex (APC). These results demonstrate that Aurora2 protein is turned over through the APC-ubiquitin-proteasome pathway. Oncogene (2000) 19, 2812 - 2819

Construction of alpha-helix peptides with beta-cyclodextrin and dansyl units and their conformational and molecular sensing properties

In order to apply de novo peptide design to molecular sensing, we designed and synthesized a-helical peptides with beta-cyclodextrin (beta-CDx) as a binding site and a dansyl unit (Dns) as a fluorescence sensing site. The conformational and molecular sensing properties of the peptides with beta-CDx and Dns in various positions were investigated. Circular dichroism and fluorescence measurements revealed that beta-CDx and Dns form intramolecular complexes which depend on their positions in the peptides. In the 17 residual peptides named EK3 and EK3R, in which beta-CDx and Dns were introduced at the fourth and the eighth positions (EK3) or at the eighth and the fourth positions (EK3R), Dns was deeply included in the CDx cavity and formed a more stable self-inclusion complex with CDx than in the peptides EK6 and EK6R, in which these moieties were at the eighth and the fifteenth positions or at the fifteenth and the eighth positions, respectively. The stability of the self-inclusion complex between beta-CDx and Dns controlled the a-helix structure as well as the binding and sensing abilities for the exogenous guests. These results demonstrate the usefulness of peptide tertiary structure for arranging CDx and other functional units, and suggest that this approach is important in the development of a new type of CDx-based sensory system.

Cyclodextrin-peptide hybrid as a hydrolytic catalyst having multiple functional groups

A designed cyclodextrin peptide hybrid, which has multiple functional groups on its alpha-helix peptide backbone, has been synthesized as a catalyst for ester hydrolysis. Kinetic study revealed that the carboxylate group plays a key role in this system.

Kinetic and mutational studies of three NifS homologs from Escherichia coli: mechanistic difference between L-cysteine desulfurase and L-selenocysteine lyase reactions

We have purified three NifS homologs from Escherichia coli, CSD, CsdB, and IscS, that appear to be involved in iron-sulfur cluster formation and/or the biosynthesis of selenophosphate. All three homologs catalyze the elimination of Se and S from L-selenocysteine and L-cysteine, respectively, to form L-alanine. These pyridoxal 5'-phosphate enzymes were inactivated by abortive transamination, yielding pyruvate and a pyridoxamine 5'-phosphate form of the enzyme. The enzymes showed non-Michaelis-Menten behavior for L-selenocysteine and L-cysteine. When pyruvate was added, they showed Michaelis-Menten behavior for L-selenocysteine but not for L-cysteine. Pyruvate significantly enhanced the activity of CSD toward L-selenocysteine. Surprisingly, the enzyme activity toward L-cysteine was not increased as much by pyruvate, suggesting the presence of different rate-limiting steps or reaction mechanisms for L-cysteine desulfurization and the degradation of L-selenocysteine. We substituted Ala for each of Cys358 in CSD, Cys364 in CsdB, and Cys328 in IscS, residues that correspond to the catalytically essential Cys325 of Azotobacter vinelandii NifS. The enzyme activity toward L-cysteine was almost completely abolished by the mutations, whereas the activity toward L-selenocysteine was much less affected. This indicates that the reaction mechanism of L-cysteine desulfurization is different from that of L-selenocysteine decomposition, and that the conserved cysteine residues play a critical role only in L-cysteine desulfurization.

Cervical myelopathy caused by C3-C4 spondylosis in elderly patients: a radiographic analysis of pathogenesis

STUDY DESIGN

A radiographic analysis of elderly patients with cervical spondylotic myelopathy, particularly those with involvement of the C3-C4 level.

OBJECTIVES

To elucidate the potential contributors to the higher incidence of pathology at C3-C4 in the elderly.

SUMMARY OF BACKGROUND DATA

In this study, the elder patients showed a greater predilection for involvement of the C3-C4 lesion compared with their younger counterparts. No previous study has addressed C3-C4 pathology in elderly patients.

METHODS

This study included 18 patients, 10 men and 8 women, with cervical spondylotic myelopathy caused by C3-C4 disorders (group I). For the purpose of comparison, 18 younger patients (less than 50 years of age) with myelopathy (group II) and 30 volunteers over the age of 65 (group III) were also investigated. Mean age at admission was 73.5 years for group I, 42.4 years for group II, and 73.4 years for group III. Radiographic analysis, using static and dynamic radiographs, was performed to evaluate the morphologic features.

RESULTS

The mean spinal canal diameter for groups I and II was significantly smaller than that for group III. Group I exhibited greater C2-C7 lordosis. The aged population, group I and group III, showed greater C3-C4 angulation associated with C4 forward inclination in neutral standing position as compared with younger patients. Regarding dynamic factors, group I showed the largest segmental motion at C3-C4, and, conversely, the smallest mobility at the lower segments, with significant differences.

CONCLUSIONS

Using radiographic analysis, morphologic features that predispose patients to disorders of the C3-C4 motion segment were evaluated. These features included 1) greater C3-C4 angulation associated with age-related postural change and 2) hypermobility at the C3-C4 segment compensating for decreased mobility at the lower segments.

cDNA cloning, purification, and characterization of mouse liver selenocysteine lyase. Candidate for selenium delivery protein in selenoprotein synthesis

Selenocysteine lyase (SCL) (EC 4.4.1.16) is a pyridoxal 5'-phosphate-dependent enzyme that specifically catalyzes the decomposition of L-selenocysteine to L-alanine and elemental selenium. The enzyme was proposed to function as a selenium delivery protein to selenophosphate synthetase in selenoprotein biosynthesis (Lacourciere, G. M., and Stadtman, T. C. (1998) J. Biol. Chem. 273, 30921-30926). We purified SCL from pig liver and determined its partial amino acid sequences. Mouse cDNA clones encoding peptides resembling pig SCL were found in the expressed sequence tag data base, and their sequences were used as probes to isolate full-length mouse liver cDNA. The cDNA for mouse SCL (mSCL) was determined to be 2,172 base pairs in length, containing an open reading frame encoding a polypeptide chain of 432 amino acid residues (M(r) 47, 201). We also determined the sequence of the N-terminal region of putative human SCL. These enzymes were shown to be distantly related in primary structure to NifS, which catalyzes the desulfurization of L-cysteine to provide sulfur for iron-sulfur clusters. The recombinant mSCL overproduced in Escherichia coli was a homodimer with the subunit M(r) of 47,000. The enzyme was pyridoxal phosphate-dependent and highly specific to L-selenocysteine (the k(cat)/K(m) value for L-selenocysteine was about 4,200 times higher than that for L-cysteine). Reverse transcriptase-polymerase chain reaction and Western blot analyses revealed that mSCL is cytosolic and predominantly exists in the liver, kidney, and testis, where mouse selenophosphate synthetase is also abundant, supporting the view that mSCL functions in cooperation with selenophosphate synthetase in selenoprotein synthesis. This is the first report of the primary structure of mammalian SCL.

Construction of HIV Rev peptides containing peptide nucleic acid that bind HIV RRE IIB RNA

Peptides containing peptide nucleic acid (PNA) have been designed and synthesized to construct molecules recognizing a bulge or a loop structure of RNA. Such peptides were here designed from the HIV Rev protein that can bind the stem-loop IIB of the Rev responsive element (RRE) RNA. Variations of PNA modulated the binding affinities of the peptides to RRE IIB RNA.

Structure of a NifS homologue: X-ray structure analysis of CsdB, an Escherichia coli counterpart of mammalian selenocysteine lyase

Escherichia coli CsdB, a NifS homologue with a high specificity for L-selenocysteine, is a pyridoxal 5'-phosphate (PLP)-dependent dimeric enzyme that belongs to aminotransferases class V in fold-type I of PLP enzymes and catalyzes the decomposition of L-selenocysteine into selenium and L-alanine. The crystal structure of the enzyme has been determined by the X-ray crystallographic method of multiple isomorphous replacement and refined to an R-factor of 18.7% at 2.8 A resolution. The subunit structure consists of three parts: a large domain of an alpha/beta-fold containing a seven-stranded beta-sheet flanked by seven helices, a small domain containing a four-stranded antiparallel beta-sheet flanked by three alpha-helices, and an N-terminal segment containing two alpha-helices. The overall fold of the subunit is similar to those of the enzymes belonging to the fold-type I family represented by aspartate aminotransferase. However, CsdB has several structural features that are not observed in other families of the enzymes. A remarkable feature is that an alpha-helix in the lobe extending from the small domain to the large domain in one subunit of the dimer interacts with a beta-hairpin loop protruding from the large domain of the other subunit. The extended lobe and the protruded beta-hairpin loop form one side of a limb of each active site in the enzyme. The most striking structural feature of CsdB lies in the location of a putative catalytic residue; the side chain of Cys364 on the extended lobe of one subunit is close enough to interact with the gamma-atom of a modeled substrate in the active site of the subunit. Moreover, His55 from the other subunit is positioned so that it interacts with the gamma- or beta-atom of the substrate and may be involved in the catalytic reaction. This is the first report on three-dimensional structures of NifS homologues.

High incidence of silent myocardial ischemia in elderly patients with non insulin-dependent diabetes mellitus

The present study was designed to reveal the incidence of silent myocardial ischemia in asymptomatic elderly non-insulin-dependent diabetic (NIDDM) patients (aged over 60 years). As a first step screening, maximal treadmill exercise test was performed. Of 140 patients studied, 54 (38.6%) were unable or not expected to achieve diagnostic levels of exercise during treadmill testing. A positive exercise test was noted in 39 of 86 (45.3%) subjects. As a second step examination, dipyridamole thallium scintigraphy was performed for 93 subjects who exhibited a positive exercise test and could not perform a maximal exercise test. Abnormal perfusion pattern was found in 39 of 93 (41.9%), who were finally considered to have a silent myocardial ischemia. Coronary angiography was performed in 18 subjects with diagnosis of silent myocardial ischemia, who gave their consent. Significant coronary artery stenosis was in fact found in 17 of 18 (94.4%) subjects studied, confirming a very high positive predictive value of this diagnostic procedure. In conclusion, elderly NIDDM patients (aged over 60 years) had an extremely high prevalence (estimated 26.3%) of silent myocardial ischemia. This evidence suggests that early and intensive detection may be needed as a part of routine care for this group.

[Epstein-Barr virus-associated hemophagocytic syndrome during mid-term pregnancy successfully treated with combined methylprednisolone and intravenous immunoglobulin]

A 32-year-old woman in the 16th week of pregnancy was admitted to our hospital because of high fever. Laboratory findings disclosed pancytopenia and extremely elevated serum LDH and ferritin levels. Coagulation tests showed disseminated intravascular coagulation. Serum soluble interleukin-2 receptor, tumor necrosis factor-alpha, and interleukin-6 levels were high, but serum interferon-gamma was below the detectable limit. Reactive Epstein-Barr virus (EBV) infection was diagnosed on the basis of a high titer of IgG antibodies to the EBV capsid antigen and early antigen. EBV was demonstrated in the peripheral blood and bone marrow cells by polymerase chain reaction. Mature histiocytosis and hemophagocytosis were detected in the bone marrow. A diagnosis of EBV-associated hemophagocytic syndrome (EBV-AHS) was made. Neither prednisolone (PSL 30 mg/day, P.O.) nor methylprednisolone (m-PSL) pulse therapy (1,000 mg/day for 3 days) induced a response. Thereafter, treatment with m-PSL pulse therapy (1,000 mg/day for 3 days) and i.v. administrations of high-dose immunoglobulin (20 g/day for 3 days) in combination with acyclovir (750 mg/day) and gabexate mesilate (2 g/day) induced remission of the disease. Maintenance therapy consisted of PSL (5 mg/day, P.O.) and camostat mesilate (600 mg/day, P.O.). The patient delivered a healthy male infant in the 35th week of pregnancy via natural birth. Reports of pregnant women with EBV-AHS are rare, and the choice of therapy has not yet been established. The present case study suggested the above combination treatment is useful and safe, and capable of changing the fulminant course of EBV-AHS during pregnancy without the use of anticancer drugs.

Distribution of JC virus DNA in peripheral blood lymphocytes of hematological disease cases

OBJECTIVE

The distribution of JC virus DNA in peripheral blood was surveyed by the polymerase chain reaction using the late genes as markers.

RESULTS

Six out of 52 cases of hematological diseases and one systemic lupus erythematosus case out of 17 cases were positive for JCV DNA. After separation into B and T lymphocytes by a cell sorter, JCV DNA was found in both cell types prepared from adult T cell leukemia and PML patients.

CONCLUSION

Only 1 or 2 copies of JCV genome were calculated to exist in a cell based on the time course analysis of PCR. Only B lymphocytes and glial brain cells are known to produce nuclear factors which support the growth of the virus. The result that B lymphocytes contained a copy number of JCV genome similar to T lymphocytes suggests that there is some barrier to viral growth in susceptible B lymphocytes, and that the growth of JCV is different from that of other virulent viruses.

Design of peptides derived from anti-IgE antibody for allergic treatment

We have designed and synthesized peptides derived from an anti-IgE antibody which has a potential for the treatment of allergy. It was indicated that conformational restriction of peptide via an intramolecular disulfide bond improved the binding affinity for IgE and that the peptide might have an ability to inhibit the IgE-receptor interaction.

A nifS-like gene, csdB, encodes an Escherichia coli counterpart of mammalian selenocysteine lyase. Gene cloning, purification, characterization and preliminary x-ray crystallographic studies

Selenocysteine lyase is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the exclusive decomposition of L-selenocysteine to L-alanine and elemental selenium. An open reading frame, named csdB, from Escherichia coli encodes a putative protein that is similar to selenocysteine lyase of pig liver and cysteine desulfurase (NifS) of Azotobacter vinelandii. In this study, the csdB gene was cloned and expressed in E. coli cells. The gene product was a homodimer with the subunit Mr of 44,439, contained 1 mol of PLP as a cofactor per mol of subunit, and catalyzed the release of Se, SO2, and S from L-selenocysteine, L-cysteine sulfinic acid, and L-cysteine, respectively, to yield L-alanine; the reactivity of the substrates decreased in this order. Although the enzyme was not specific for L-selenocysteine, the high specific activity for L-selenocysteine (5.5 units/mg compared with 0.019 units/mg for L-cysteine) supports the view that the enzyme can be regarded as an E. coli counterpart of mammalian selenocysteine lyase. We crystallized CsdB, the csdB gene product, by the hanging drop vapor diffusion method. The crystals were of suitable quality for x-ray crystallography and belonged to the tetragonal space group P43212 with unit cell dimensions of a = b = 128.1 A and c = 137.0 A. Consideration of the Matthews parameter Vm (3.19 A3/Da) accounts for the presence of a single dimer in the crystallographic asymmetric unit. A native diffraction dataset up to 2.8 A resolution was collected. This is the first crystallographic analysis of a protein of NifS/selenocysteine lyase family.

Thrombomodulin levels in patients with coronary artery disease

We investigated the association between the serum level of thrombomodulin and known coronary risk factors in 119 men who underwent coronary angiography. Total cholesterol level was significantly higher in patients with coronary atherosclerosis than in those without. Significantly higher frequency of hypertension was noted in patients with coronary atherosclerosis. Uric acid level and frequency of smoking tended to be higher in patients with coronary atherosclerosis but the differences were short short of the significant level. The serum level of thrombomodulin between patients with coronary atherosclerosis and those without was not statistically significant. Age, blood urea nitrogen, and creatinine were positively correlated and creatinine clearance was inversely correlated with the serum level of thrombomodulin. Serum levels of total cholesterol, triglyceride, high-density lipoprotein cholesterol, uric acid, and fasting blood sugar, plasma level of fibrinogen, and body mass index were not related to the serum level of thrombomodulin. There was no significant correlation between the severity of coronary atherosclerosis, hypertension, alcohol use, or smoking and the serum level of thrombomodulin. Restenosis was present in 8 of 16 patients who underwent percutaneous transluminal coronary angioplasty and had a follow-up angiogram at 6.0 +/- 3.0 months. Univariate analysis revealed no significant difference in the thrombomodulin level with and without restenosis. The present findings suggest that elevated thrombomodulin levels in patients with coronary artery disease may reflect retention of thrombomodulin due to decrease in thrombomodulin clearance in the kidney.

Optimization of hydrophobic domains in peptides that undergo transformation from alpha-helix to beta-fibril

Recent studies on peptide fibrillogenesis by the de novo method as well as amyloidogenic proteins including prion proteins and Alzheimer's beta-peptides have provided insights into the conformational changes, such as alpha-helix to beta-structure, involved in folding and misfolding processes. We have found that an exposed hydrophobic nucleation domain at N-terminal causes a structural transition of a peptide from alpha-helix to beta-fibril. It became clear that N-terminal acyl groups of particular lengths in a 2alpha-helix peptide caused the peptide to undergo an alpha-to-beta transition. The peptide with the octanoyl group (C8-2alpha) showed the highest rate of transformation. The study of the designed peptides revealed that these alpha-to-beta transitions were closely related to the initial alpha-helix conformation and its stability. Engineering peptides that undergo alpha-to-beta transitions are attractive not only to the study of pathogenic proteins such as prion proteins, but also to the control of self-assembly of peptides, which will lead to the development of peptidyl self-assembling materials.

A method of RF inhomogeneity correction in MR imaging

A direct postprocessing method for correcting RF inhomogeneity in MR imaging is proposed. First, two images with different flip-angles of theta and 2theta are obtained. Next, the spatial distribution maps of the sensitivity of the surface coil and the B1 field intensity are produced by employing those images. Finally, the correction of the MR image is achieved, dividing the original image by distribution maps of the coil sensitivity and the B1 field intensity. The method was applied to images obtained by a gradient echo sequence and the corrected image is presented.

Design of novel porphyrin-binding peptides based on antibody CDR

Novel porphyrin-binding peptides were designed on the basis of an antigen binding site of an antiheme monoclonal antibody. Synthetic peptides were modified with a pyrene moiety. The spectroscopic measurements revealed that the synthetic peptides bound a porphyrin effectively.

Use of temporary vena cava filters after catheter-directed fragmentation and thrombolysis in patients with acute pulmonary thromboembolism

Acute pulmonary thromboembolism is a life-threatening disease and in almost all cases originates from deep venous thrombosis in the proximal deep venous system of the legs. In order to prevent further episodes of thromboembolism in 2 patients with acute pulmonary thromboembolism, we inserted an Antheor temporary vena cava filter after catheter-directed fragmentation and thrombolysis. No complications occurred during the insertion of the filters and our results suggest that this filter device may be clinically safe and effective for temporary protection against pulmonary thromboembolism.

Structure and property of model peptides of proline/arginine-rich region in bactenecin 5

Bactenecin 5 (Bac 5), a cationic antibacterial peptide, contains a repeating region of Arg-Pro-Pro-X (X = hydrophobic residue). To investigate the structure and property of a Pro/Arg-rich region, we synthesized a series of repeating peptides, Ac-(Arg-Pro-Pro-Phe)n-NHCH3 (n = 2, 4, 6, 8 and 10) (PR2, PR4, PR6, PR8 and PR10) as models. The circular dichroism (CD) study suggested that the peptides with longer repeats, PR6, PR8 and PR10, formed a conformation similar to poly(proline)-II in aqueous solution. The CD spectra did not change in the presence of dipalmitoyl-DL-alpha-phosphatidylcholine (DPPC), but they changed in the presence of DPPC/ dipalmitoyl-DL-3-phosphatidylglycerol (DPPG). The gamma-helix, which is very similar in conformation to the poly(proline)-II helix, had the lowest energy conformation for the peptides by energy calculations. Peptides PR6, PR8 and PR10 caused slight leakage of fluorescent dye entrapped in DPPC vesicles, and in the presence of DPPC/DPPG, these peptides showed a considerable level of dye-leakage activity. In contrast, the shorter peptides PR2 and PR4 showed no activity. The same tendency was found in measurements of membrane-fusion activity. Judging from these results, the repeating region of Bac 5 may make a framework to hold a conformation resembling the poly(proline)-II structure in aqueous solution. In addition, this region may interact with acidic lipids, resulting in a change in conformation of the peptide.

Interaction of alpha-helical peptides with phospholipid membrane: effects of chain length and hydrophobicity of peptides

To investigate the interaction of amphiphilic alpha-helical peptides with phospholipid membranes, we synthesized Ac-(Leu-Ala-Arg-Leu)3-NHCH3 (4[3]) and three derivatives, in which the chain length and the size of the hydrophobic region of the peptides were different from each other. These peptides formed an alpha-helical structure in the presence of vesicles. In the membrane-perturbation measurement, only 43 showed a strong membrane-perturbation activity below phase-transition temperature (25 degrees C), but above phase-transition temperature (50 degrees C), most peptides showed similar strong activities. On the other hand, in membrane-fusion measurement the long peptides, e.g., Ac-(Leu-Ala-Arg-Leu)3-(Leu-Arg-Ala-Leu)3-NHCH3, had strong activities at low peptide concentrations at 25 degrees C. The present study indicated a parallel relationship did not always exist between membrane fusion and perturbation caused by peptides.