Bacterial cysteine desulfurases: their function and mechanisms

Cysteine desulfurase is a pyridoxal 5'-phosphate (PLP)-dependent homodimeric enzyme that catalyzes the conversion of L-cysteine to L-alanine and sulfane sulfur via the formation of a protein-bound cysteine persulfide intermediate on a conserved cysteine residue. Increased evidence for the functions of cysteine desulfurases has revealed their important roles in the biosyntheses of Fe-S clusters, thiamine, thionucleosides in tRNA, biotin, lipoic acid, molybdopterin, and NAD. The enzymes are also proposed to be involved in cellular iron homeostasis and in the biosynthesis of selenoproteins. The mechanisms for sulfur mobilization mediated by cysteine desulfurases are as yet unknown, but enzymes capable of providing a variety of biosynthetic pathways for sulfur/selenium-containing biomolecules are probably applicable to the production of cofactors and the bioconversion of useful compounds.

Cutaneous sarcoidosis successfully treated with topical tacrolimus

Sarcoidosis is a disorder characterized by macrophage- and T-cell-mediated responses to as yet unidentified infectious antigens or autoantigens. We describe a 62-year-old woman with a 10-year history of orange-yellow plaques of sarcoidosis on her face. Her cutaneous lesions responded to topical tacrolimus ointment after unsuccessful treatment with topical and systemic corticosteroids. No adverse effects were noted with topical tacrolimus in this patient. We discuss the mode of action by which this immunosuppressive agent may act against sarcoidosis.

Up-regulation of the urokinase-type plasminogen activator receptor by monocyte chemotactic proteins

The urokinase-type plasminogen activator receptor (uPAR) is a multifunctional molecule involved in migration and adhesion of leukocytes to sites of inflammation. Based on our hypothesis that a chemoattractant can stimulate uPAR expression by its target cell, thereby promoting cell migration, we employed three chemokines [monocyte chemotactic protein (MCP)-1, MCP-2 and MCP-3] as chemoattractants, and examined their effect on uPAR expression in a human monocyte-like cell line, U937. Northern blot analysis demonstrated that all three chemokines tested increased the level of uPAR mRNA in time-dependent and dose-dependent manners. Among them, MCP-3 exhibited the most potent effect. Scatchard analysis showed that incubation with MCP-3 (1 x 10(-8) mol/l) for 16 h resulted in a significant increase in the number of uPAR from (6.8 +/- 0.3) x 10(3) to (10.3 +/- 1.6) x 10(3)/cell, and in a slight increase in the equilibrium dissociation constant, K(d). The effect of anti-uPAR antibodies on MCP-3-induced U937 cell migration across an endothelial cell monolayer and a type I collagen layer was assessed by means of the modified Boyden chamber assay. Although MCP-3 caused a three-fold increase in migration, incubation with an antibody to uPAR markedly abrogated the induced cell migration. These results support our hypothesis and suggest that up-regulation of uPAR in target cells might be an important and common feature of chemoattractants.

Expression of endothelial cell-associated molecules in AML cells

Recently, it has been clarified that interaction between hematopoietic cells and endothelial cells is important in normal hematopoiesis and leukemogenesis. In this study, we examined the relationship between AML cells and endothelial cells by analyzing the expression profile of angiogenic factors, angiopoietin-1 (Ang-1), Ang-2, Tie-2 (a receptor for angiopoietins) and vascular endothelial growth factor (VEGF). Our results demonstrated that CD7(+)AML expressed Ang-2 mRNA frequently and integrin-family adhesion molecules (CD11c and CD18) intensively, suggesting the close correlation with endothelial cells. On the other hand, in t(8;21) AML cells, expression of Ang-2 was infrequent and expression of integrin-family adhesion molecules (CD11b, CD11c and CD18) was weak, suggesting the sparse association with endothelial cells. As for CD7(+)AML cells, despite the frequent and intense expression of endothelial cell-associated molecules (such as Ang-2, CD11c and CD18), intensity of Tie-2 expression was quite low (P < 0.05). Ang-2 expressed in CD7(+)AML cells is not considered to act in an autocrine fashion, but to work on endothelial cells to "feed" leukemic cells. Although Ang-2 is recognized as a natural antagonist for Tie-2, our data presented here suggested the alternative role of Ang-2 in the relationship between endothelial cells and leukemia cells, at least in a subset of leukemia such as CD7(+)AML. These results were supported by the study using AML cell lines, KG-1 (CD7 negative) and its subline KG-1a (CD7 positive); KG-1 had mRNA expression profile of Ang-1(+)Ang-2(-)Tie-2(+), while KG-1a showed Ang-1(+)Ang-2(+)Tie-2(-). These difference in the expression profile of angiogenic factors between CD7(+)AML and t(8;21)AML may explain the characteristic morphological features of these leukemias (CD7(+)AML as blastic type and t(8;21)AML as differentiative type).

Follow-up study of conservative treatment for atlantoaxial rotatory displacement

Rotatory displacement of the atlantoaxial joint is one of the causes of torticollis in children. Some of these cases show persistent symptoms and may lead to rotatory fixation; however, only a few studies have been directed to the prognosis of atlantoaxial rotatory displacement after conservative treatment. Clinical and radiographic reviews were performed in 35 patients (16 male and 19 female) with rotatory displacement of the atlantoaxial joint. The mean age at admission was 6.5 (range: 2-12) years old, and the mean follow-up period was 3.4 (1.4-5.8) years. All patients successfully achieved reduction after 2 to 3 weeks of continuous halter traction; however, 9 patients (25.7%) experienced recurrence, and 7 patients (20.0%) had a slight torticollis at follow-up. The duration of symptoms before treatment affected the recurrence rate, and the torticollis was apt to remain in cases with severe displacement at admission.

Cervical posterior fusion with wave-shaped rod under local anesthesia for cervical spondylotic myelopathy: review of 12 patients

STUDY DESIGN

Clinical evaluation of cervical interspinous fusion under local anesthesia in elderly patients with cervical spondylotic myelopathy.

OBJECTIVES

To evaluate the effectiveness of cervical posterior fusion with wave-shaped rods inserted under local anesthesia for elderly high-risk patients with cervical spondylotic myelopathy.

SUMMARY OF BACKGROUND DATA

A substantial number of patients cannot undergo surgical interventions under general anesthesia because of their general medical complications. Although such patients would become unable to walk, which might induce a worsening of their general condition, conservative treatments had been adopted as the only treatment for these patients. The authors have obtained satisfactory results by means of posterior interspinous fusion under local anesthesia even in the high-risk patients with severe cervical spondylotic myelopathy. The aims of this surgical technique were to adjust cervical alignment and to stabilize the motion segment(s) without decompression.

PATIENTS AND METHODS

Between May 1989 and August 1998, 12 elderly patients (3 men and 9 women) with cervical spondylotic myelopathy were treated with posterior interspinous fusion using wave-shaped rods inserted under local anesthesia. The average age at the surgery was 76.9 years. The average follow-up period was 5 years 6 months. All patients were unable to walk without any assistance because of their advanced myelopathy. It was felt that all of them would be unable to accept general anesthesia because of their generally poor medical conditions. Preoperative severity of the clinical symptoms and postoperative recovery were evaluated by a scoring system proposed by the Japanese Orthopaedic Association, which had 17 points at full mark.

RESULTS

The average duration of the surgical procedure was 122.8 minutes. The average total blood loss was 118.6 g. No instrument failures were denoted. Neither neural deterioration nor major complication was observed relating to the surgery. Radiographic bony union of the grafted bone was achieved in all patients. Progression of myelopathy was arrested in all 12 patients, and clinical symptoms were improved in 10 patients. The mean Japanese Orthopaedic Association scores had increased from 5.0 to 10.2 points.

CONCLUSIONS

Twelve high-risk patients with cervical spondylotic myelopathy were treated with posterior interspinous fusion using wave-shaped rods inserted under local anesthesia. This method was evaluated as an effective surgical salvage without any mortal complications even in the elderly high-risk patients.

Construction of peptides with nucleobase amino acids: design and synthesis of the nucleobase-conjugated peptides derived from HIV-1 Rev and their binding properties to HIV-1 RRE RNA

In order to develop a novel molecule that recognizes a specific structure of RNA, we have attempted to design peptides having L-alpha-amino acids with a nucleobase at the side chain (nucleobase amino acid (NBA)), expecting that the function of a nucleobase which can specifically recognize a base in RNA is regulated in a peptide conformation. In this study, to demonstrate the applicability of the NBA units in the peptide to RNA recognition, we designed and synthesized a variety of NBA-conjugated peptides, derived from HIV-1 Rev. Circular dichroism study revealed that the conjugation of the Rev peptide with an NBA unit did not disturb the peptide conformation. RNA-binding affinities of the designed peptides with RRE IIB RNA were dependent on the structure of the nucleobase moieties in the peptides. The peptide having the cytosine NBA at the position of the Asn40 site in the Rev showed a higher binding ability for RRE IIB RNA, despite the diminishing the Asn40 function. Furthermore, the peptide having the guanine NBA at the position of the Arg44 site, which is the most important residue for the RNA binding in the Rev, bound to RRE IIB RNA in an ability similar to Rev34-50 with native sequence. These results demonstrate that an appropriate NBA unit in the peptide plays an important role in the RNA binding with a specific contact such as hydrogen bonding, and the interaction between the nucleobase in the peptide and the base in the RNA can enhance the RNA-binding affinity and specificity.

HIV Rev peptides conjugated with peptide nucleic acids and their efficient binding to RRE RNA

HIV Rev peptides conjugated with peptide nucleic acids (PNAs) were designed and synthesized to develop a designing approach for a novel RNA-binding molecule. The binding affinities of PNA-peptides with the Rev responsive element (RRE) RNA were determined by the competition assay using a rhodamine-labeled Rev. The peptide conjugated with an antisense PNA (TGCGC) bound RRE RNA more efficiently than the molecule without the PNA or the peptide sequence.

Construction of peptide conjugates with peptide nucleic acids containing an anthracene probe and their interactions with DNA

We designed and synthesized the peptide nucleic acid (PNA)-peptide conjugates having anthracene chromophores and investigated their interactions with calf thymus DNA, [d(AT)(10)](2), [d(GC)(10)](2), and [d(AT)(10)dA(6)](2). Considering the synthesis compatibility and expecting that a novel DNA analogue, PNA, can improve DNA binding properties of alpha-helix peptides, we attempted to attach thymine PNA oligomers at the C-terminus of a 14 amino acid alpha-helix peptide that contained a pair of artificial intercalators, anthracene, as a probe, and to examine their interactions with DNA using anthracene UV, fluorescence and circular dichroism properties. The results observed in this study showed that the designed peptide folded in an alpha-helix structure in the presence of calf thymus DNA, [d(AT)(10)](2), and [d(AT)(10)dA(6)](2) with the chromophores at the side-chain being fixed with a left-handed chiral-sense orientation. The alpha-helix and the anthracene signals were not observed for [d(GC)(10)](2). Incorporation of thymine PNA oligomers into the designed alpha-helix peptide increased the DNA binding ability to [d(AT)(10)dA(6)](2) with increasing the length of the PNA without changing the conformations of the peptide backbone and the anthracene side-chains.

Biomechanical comparison of posterior cervical fixation

STUDY DESIGN

Biomechanical stability using four different posterior cervical fixation techniques was evaluated in human cadaveric spine.

OBJECTIVES

To introduce an alternative interspinous fixation technique using wavy-shaped rods, and to compare its in vitro biomechanical stability with that of other posterior cervical fixation techniques.

SUMMARY OF BACKGROUND DATA

Fixation of the posterior cervical spine with interspinous wiring is well known as Rogers' or Bohlman's technique. Recently, several plate fixation techniques have been used for posterior cervical stabilization. Since 1983, the authors have developed the wavy-shaped rod system as an alternative to the interspinous fixation technique. This unique technique has been proven clinically useful in Japan. However, the authors are not aware of any prior biomechanical studies.

METHODS

Seven fresh frozen cervical human spines were tested at the C5-C6 motion segment. Nondestructive static biomechanical testing was performed with flexion-extension, lateral bending, and axial rotation for the following stabilization techniques: intact spine, creation of a Stage 3 distractive-flexion injury followed by fixation with the wavy-shaped rods bounded by three multistrand cables, interspinous wiring with a multistrand cable, triple wiring technique using multistrand cables with a pair of unicortical grafts from the ilium, and lateral mass plate fixation with Magerl's screw technique. Testing was performed on a material testing machine (MTS 858 Bionix test system, MTS, Minneapolis, MN), and load displacement curves were obtained using four linear extensometers and one rotatory extensometer across the C5-C6 motion segment.

RESULTS

In axial compression loading, the reconstructed specimens showed significant differences in range of motion measured at the anterior and posterior positions, and statistical analysis was performed using one-way analysis of variance. In a comparison of the four fixation techniques, the construct with the wavy-shaped rod indicated significantly less motion both anteriorly and posteriorly than with the other fixation techniques. Also in flexion-extension loading, all the techniques significantly limited the intervertebral motion below the level of the intact motion segment. Particularly, the construct with the wavy-shaped rod showed the smallest mobility, 49.9% anteriorly and 9.3% posteriorly, compared with that of the intact spine. In lateral bending, the lateral mass plate provided the greatest stability, which was superior to the intact segment, but the difference was not statistically significant. In axial rotation, all the reconstruction techniques limited the angular motion below the intact level (wavy rod, 68.0%; Rogers' wiring, 75.2%; Bohlman's triple wiring, 59.8%; lateral mass plate, 71.7%), but no significant differences were observed using one-way analysis of variance, as compared with the intact segment.

CONCLUSIONS

All four reconstruction techniques restored the stability of the cervical motion segment to at least the level of the intact motion segment before destabilization. An alternative cervical posterior fixation technique, the Wavy Rod system, was considered the most effective technique in stabilizing a cervical motion segment, particularly in axial compression and flexion extension loading.

Multipeptide-metalloporphyrin assembly on a dendrimer template and photoinduced electron transfer based on the dendrimer structure

To construct an artificial photosynthetic system, peptide dendrimers [n-(X-HLY)PAMAMs: X = R, E; Y= L, F; n=4, 8, 16, 32 and 64 segments], in which amphiphilic alpha-helix peptides (X-HLY: R-HLL, E-HLL and R-HLF) were introduced at the end groups of polyamidoamine dendrimers (PAMAMs), were designed and synthesized. The peptide dendrimers 64-(X-HLY)PAMAMs are novel synthetic biopolymers with an enormous molecular weight, about 160 kDa, and with a regulated amino acid sequence and three-dimensional conformation. The peptide dendrimers bound Fe(III)- or Zn(II)-mesoporphyrin IX per two alpha-helices; this afforded a multimetalloporphyrin assembly similar to the natural light-harvesting antennae in photosynthetic bacteria. Circular dichroism studies and peroxidase activity measurements revealed that metalloporphyrins were coordinated to the peptide dendrimers in a regulated manner and packed more densely with the growth of the dendrimer generation. Fluorescence quenching and photoreduction studies with methylviologen demonstrated that the photoinduced electron-transfer function with the peptide dendrimer-multi-Zn-MP was accomplished more effectively as the dendrimer generation increased. Thus, the three-dimensional assembly of metalloporphyrins and peptides in the dendrimer was an effective module for light-harvesting antennae in an artificial photosynthetic system.

Malignant lymphoma of the bone associated with systemic sarcoidosis

A 57-year-old woman was hospitalized with malignant lymphoma of the right talus. After treatment, complete remission was obtained. Gallium-67 scintigraphy to confirm the remission demonstrated increased uptake in the whole body skeletal muscle, especially in her thighs. Biopsy of right gastrocnemius muscle showed epithelioid granuloma. Serum angiotensin-converting enzyme activity (ACE) and lysozyme had increased to several times the normal range. We diagnosed her disease as bone-associated sarcoidosis-lymphoma syndrome. Human herpes virus 8 (HHV-8) genome was examined in the bone marrow specimen, and the relationship between sarcoidosis-lymphoma syndrome and HHV-8 was discussed.

Long-term follow-up results of anterior interbody fusion applied for cervical myelopathy due to ossification of the posterior longitudinal ligament

STUDY DESIGN

A long-term follow-up study was carried out in 30 patients who underwent anterior interbody fusion for cervical myelopathy associated with ossification of the posterior longitudinal ligament (OPLL).

OBJECTIVE

To investigate whether anterior interbody fusion without decompression is an appropriate surgical method for long-term relief of cervical OPLL myelopathy.

SUMMARY OF BACKGROUND DATA

Several studies of operative results after posterior decompression for cervical myelopathy due to ossification of the posterior longitudinal ligament have been reported. There has been no report about anterior interbody fusion without decompression. The postoperative results of this treatment method applied in cervical OPLL myelopathy have been evaluated by the authors of the present study for more than 10 years. No reports on such a long-term follow-up study have been published in the literature.

METHODS

Thirty patients who underwent anterior interbody fusion for cervical OPLL myelopathy were evaluated clinically and radiographically. The mean follow-up period was 14.7 years (range, 10-23 years).

RESULTS

Clinical results were evaluated according to Okamoto's classification. At the time of the final follow-up evaluation, 16 patients had improved in functional score by two grades, and their surgical results were regarded as excellent; eight patients improved by one grade, and their clinical outcomes were regarded as good; five patients showed no change; and the condition of one patient deteriorated. As for radiographic analysis, the type of ossification had changed in four cases. Ossification width and thickness increased in 26 patients. Postoperative alignment of the cervical spine showed kyphosis in three patients, straight spine in 11 patients, and lordosis in 16 patients.

CONCLUSION

Anterior interbody fusion without decompression is an effective treatment for cervical OPLL myelopathy that resulted in stable long-lasting conditions.

Hypertrophy of the posterior longitudinal ligament is a prodromal condition to ossification: a cervical myelopathy case report

STUDY DESIGN

A histopathologic examination of a specimen that showed hypertrophy of the posterior longitudinal ligament of the cervical spine.

OBJECTIVES

To illustrate the possibility of hypertrophy of the posterior longitudinal ligament as a prodromal condition to ossification of the posterior longitudinal ligament.

SUMMARY OF BACKGROUND DATA

Despite much study, the pathology of ossification of the posterior longitudinal ligament still remains unclear. Hypertrophic change often is seen in the part of the ossified ligament; however, there have been few histopathologic reports on hypertrophy of the posterior longitudinal ligament. Some reports have suggested that hypertrophy of the posterior longitudinal ligament is a prodrome of ossification of the posterior longitudinal ligament.

METHODS

A 64-year-old man was admitted to the hospital because of gait disturbance and developed oliguria. In a plain radiograph, segmental ossification of the posterior longitudinal ligament was found at C4, C5, and C6. Computed tomograph myelogram revealed a soft tissue shadow, maximum 3.8 mm in diameter, on the dorsal side of the ossification of the posterior longitudinal ligament at C5 and C6. Magnetic resonance T1-weighted image (T1WI) showed an equivalent signal with the intervertebral disc on the dorsal side of ossification of the posterior longitudinal ligament. This lesion was enhanced with Gd-DTPA and confirmed as hypertrophy of the posterior longitudinal ligament. Cervical anterior decompression and fusion were performed using Yamaura's technique. The ossified and thickened lesion was elevated and removed en bloc. Then, hematoxylin-eosin and toluidine blue staining was performed to detect metachromasia.

RESULTS

Macroscopic examination of the specimen revealed that soft tissue formation was connected with the C4-C5 intervertebral space and extended downward to C6-C7. Histopatholgically, collagen fibers were proliferating in the long-axis direction on both ventral and dorsal sides. This was surrounded by extended nucleus pulposus-like chondrocyte tissue, where endplate cartilage was detected around the C4 pedicle. Roux staining was low, and partial vascular and cellular infiltration was observed, although it was not marked.

CONCLUSION

The herniated nucleus pulposus involving endplate cartilage from C4-C5 was limited to the superficial layer, and proliferation of nucleus pulposus-like chondrocytes occurred in the herniated tissue, where they might undergo a change in cell phenotype. The results of the present study support the hypothesis that hypertrophy of the posterior longitudinal ligament is a prodromal condition to ossification of the posterior longitudinal ligament.

Removal of soluble selenium by a selenate-reducing bacterium Bacillus sp. SF-1

In order to develop a biological process for removal of selenium from industrial wastewater, Bacillus sp. strain SF-1 was isolated from selenium-contaminated sediment. The bacterium reduces selenate to selenite and subsequently to nontoxic insoluble elemental selenium using lactate as an electron donor and selenate as an electron acceptor in an anaerobic condition. Elemental selenium transformed from soluble selenium was deposited both inside and outside of the cells. Since the selenate reduction rate of the strain SF-1 was higher than the selenite reduction rate, selenite was transiently accumulated. In an experiment of the repeated soluble selenium reduction by strain SF-1, 0.5 mM of selenate was sequentially treatable with a cycle of one day. Thus, our sequential system for removal of soluble selenium is very useful.

Design and synthesis of 3?-helix peptides forming a cavity for a fluorescent ligand

As a model of receptor protein, a series of 3alpha-helix bundle peptides constructed on a template peptide were designed so as to possess a hydrophobic cavity. The size of cavity was modulated by simple replacements of Leu residues to Ala residues in the hydrophobic core. Binding abilities to 8-anilino-1-naphthalenesulfonic acid (ANS) were estimated by the increase of fluorescence intensity. The peptide having three or four Ala residues in the hydrophobic core remarkably increased the binding ability for ANS, though the peptide having two Ala residues gave an inefficient cavity for ANS. The peptide having six Ala residues decreased the binding ability due to crucial destabilization of the helix bundle structure. This scaffold can be utilized to a receptor model, while further tuning of the sequence is necessary.

Photoinduced hydrogen evolution with peptide dendrimer-multi-Zn(II)-porphyrin, viologen, and hydrogenase

To construct an artificial photosynthetic system, multi-Zn(II)-mesoporphyrins in peptide dendrimers were equipped as a photosensitizer of photoinduced hydrogen evolution in a four-component system (electron donor, photosensitizer, electron carrier, and catalyst), so that hydrogen was evolved effectively by the dendrimer architecture, for the first time. The hydrogen evolution activity was correlated to the photoreduction ability of viologen by the Zn-porphyrin-peptide dendrimers. Additionally, using positively charged methyl-viologen as an electron carrier, the photoinduced hydrogen evolution function with the positively charged peptide dendrimer was superior to that with the negatively charged peptide dendrimer, despite that the positive dendrimer did not strongly bind the positively charged methyl-viologen with the electrostatic interaction. By contrast, when zwitterionic propylviologen sulfonate was used, photoreduction and hydrogen evolution properties were identical between the positively and the negatively charged dendrimers. These results demonstrated that the dynamic interaction between the positive dendrimer and methyl-viologen was preferable for the photoreduction and hydrogen evolution, and that the three-dimensional assembly of Zn(II)-mesoporphyrins using the peptide dendrimers was effective as a photosensitizer in the artificial photosynthesis.

Design, synthesis and peroxidase-like activity of 3alpha-helix proteins covalently bound to heme

As a model of artificial peroxidase, de novo designed three-alpha-helix proteins, 3alpha-H9 and 3alpha-H12, covalently bound to Fe(III)-mesoporphyrin IX were synthesized and examined for a peroxidase-like activity. The activity was regulated according to the positions of His residues in the proteins, and the His residues played a role in an acid-base catalytic function.

Gene cloning, purification, and characterization of two cyanobacterial NifS homologs driving iron-sulfur cluster formation

Iron-sulfur proteins are essential in the photosynthetic system and many other biological processes. We have isolated and characterized enzymes driving the formation of iron-sulfur clusters from Synechocystis sp. PCC6803. Two genes (slr0387 and sll0704), showing similarity to nifS of Azotobacter vinelandii, were cloned, and their gene products (SsCsdl and SsCsd2) were purified. They catalyzed the desulfuration of L-cysteine. Reconstitution of a [2Fe-2S] cluster of cyanobacterial ferredoxin proceeded much faster in the presence of L-cysteine and either of these enzymes than when using sodium sulfide. These results suggest that SsCsdl and SsCsd2 facilitate the iron-sulfur cluster assembly by producing inorganic sulfur from L-cysteine. Synechocystis sp. PCC6803 has no gene coding for a protein with similarity to the N-terminal domain of NifU of A. vinelandii, which is believed to cooperate with NifS to assemble iron-sulfur clusters. Thus, the cluster formation in the cyanobacterium probably proceeds through a mechanism that is different from that in A. vinelandii.

Construction of two-stranded alpha-helix peptides based on influenza virus M1 protein selectively bound to RNA

Various 2alpha-helix peptides were designed and synthesized based on the RNA-binding region of matrix protein M1 in influenza virus. The binding properties of the peptides to model ssRNA, ssDNA, dsDNA, and virus RNA were examined by the fluorescence studies of a dansyl group incorporated into the peptides. The peptide containing the hydrophilic residues of M1 RNA-binding region bound RNAs selectively.

Mutational analysis of designed peptides that undergo structural transition from alpha helix to beta sheet and amyloid fibril formation

BACKGROUND

Conformational alteration and fibril formation of proteins have a key role in a variety of amyloid diseases. A simplified model peptide would lead to a better understanding of underlying mechanisms whereby protein misfolding and aggregation occur. Recently, we reported the design of peptides that undergo a self-initiated structural transition from an alpha helix to a beta sheet and form amyloid fibrils. In this study, we focus on two glutamine residues in the peptide, and report a mutational analysis of these residues.

RESULTS

A coiled-coil alpha-helix structure bearing a hydrophobic adamantanecarbonyl (Ad) group at the N terminus was designed (parent peptide Ad-QQ). In neutral aqueous solution, the double Gln-->Ala mutant (Ad-AA) underwent the alpha-->beta structural transition within four hours, which was similar to the case of Ad-QQ. In contrast, two kinds of single Gln-->Ala mutant (Ad-QA and Ad-AQ) required three days for the transition. Furthermore, Ad-QQ and Ad-AA formed amyloid fibrils, whereas Ad-QA and Ad-AQ did not. Interestingly, however, Ad-QA and Ad-AQ complementarily assembled into the fibrils when they were mixed.

CONCLUSIONS

The Gln-->Ala substitution in the peptide significantly alters the alpha-->beta transitional properties and the ability to form amyloid fibrils. A heterogeneous assembly of two peptide species into the fibrils is also presented. These results suggest that the secondary structural transition and self-assembly into the well-organized fibril may depend strictly on the primary structure, which determines the beta-sheet packing. The results might provide insights into misfolding and fibril formation of disease-associated mutant proteins.