Gene structure, intracellular localization, and functional roles of sterol carrier protein-2

Since its discovery three decades ago, sterol carrier protein-2 (SCP-2) has remained a fascinating protein whose physiological function in lipid metabolism remains an enigma. Its multiple proposed functions arise from its complex gene structure, post-translational processing, intracellular localization, and ligand specificity. The SCP-2 gene has two initiation sites coding for proteins that share a common 13 kDa SCP-2 C-terminus: (1) One site codes for 58 kDa SCP-x which is partially post-translationally cleaved to 13 kDa SCP-2 and a 45 kDa protein. (2) A second site codes for 15 kDa pro-SCP-2 which is completely post-translationally cleaved to 13 kDa SCP-2. Very little is yet known regarding how the relative proportions of the two transcripts are regulated. Although all three proteins contain a C-terminal SKL peroxisomal targeting sequence, it is unclear why all three proteins are not exclusively localized in peroxisomes. However, the recent demonstration that the SCP-2 N-terminal presequence in pro-SCP-2 dramatically modulated the intracellular targeting coded by the C-terminal peroxisomal targeting sequence may account for the observation that as much as half of total SCP-2 is localized outside the peroxisome. The tertiary and secondary structure of the 13 kDa SCP-2, but not that of 15 kDa pro-SCP-2 and 58 kDa SCP-x, are now resolved. Increasing evidence suggests that the 58 kDa SCP-x and 45 kDa proteins are peroxisomal 3-ketoacyl-CoA-thiolases involved in the oxidation of branched chain fatty acids. Since 15 kDa pro-SCP-2 is post-translationally completely cleaved to 13 kDa SCP-2, relatively little attention has been focused on this protein. Finally, although the 13 kDa SCP-2 is the most studied of these proteins, because it exhibits diversity of its ligand partners (fatty acids, fatty acyl CoAs, cholesterol, phospholipids), new potential physiological function(s) are still being proposed and questions regarding potential compensation by other proteins with overlapping specificity are only beginning to be resolved.

Sustained and complete phenotype correction of hemophilia B mice following intramuscular injection of AAV1 serotype vectors

We previously reported that direct intramuscular injection of non-serotype-2 AAV vectors, especially AAV serotype 1 (AAV1), resulted in expression of supranormal levels of canine F9 in immunodeficient mice. Here we test the ability of the AAV1-F9 vector to deliver sustained expression and correction of factor IX (FIX) deficiency in genetically engineered hemophilic mice. Intramuscular injection of AAV1-F9 resulted in 100-1000 times more canine F9 in plasma of recombinant AAV1-F9 mice compared with injection of AAV2-F9. Assessment of clotting activity by activated partial thromboplastin time confirmed that circulating canine FIX was indeed functional. Moreover, phenotypic correction assayed by tail clip challenge resulted in survival of all AAV1-F9 treated animals, in contrast to naive mice and 50% of AAV2-treated hemophilia B mice, which failed to survive. Administration of cyclophosphamide (CTX) was required to suppress formation of anti-canine FIX antibodies for AAV2-treated animals, whereas it was dispensable for those treated with AAV1-F9. This difference in immunogenicity further emphasizes the usefulness of serotype-specific vectors. Finally, we report that correction of the hemophilia phenotype using AAV1-F9 was complete and persistent (over 8 months), a result that underscores the value of continued exploration of alternative AAV serotype vectors.

Induction of tolerance to human factor VIII in mice

This paper reports loss of human factor VIII (hFVIII) inhibitory antibody in immunocompetent C57BL/6 mice. High-titer anti-hFVIII antibody developed in the mice within 7 to 14 days of intraportal administration of adeno-associated virus (AAV) carrying FVIII that coincided with a reduction in plasma hFVIII antigen. Bethesda titers (> 100 units) persisted relatively unchanged for 9 to 10 months. Unexpectedly, at 10 months after injection of the virus, hFVIII protein (up to 59 ng/mL) was detected in 3 mice at the same time as disappearance of hFVIII inhibitor. The level of hFVIII was similar to that found in immunodeficient mice receiving the same dose of recombinant AAV carrying hFVIII without hFVIII inhibitor. These results suggest that tolerance to hFVIII can be induced by sustained expression of hFVIII in a mouse model. Further elucidation of this observation may affect use of FVIII gene transfer in the treatment of inhibitor-positive patients with hemophilia A.

[Bax gene expression in endometrial carcinoma]

OBJECTIVE

To study the relationship between bax gene expression and endometrial carcinoma.

METHODS

Bax mRNA expression was evaluated by RT-PCR in a series of 8 normal proliferative endometrium (NPE), 6 simple and complex hyperplasia (SCH), 6 atypical hyperplasia (AH) and 42 endometrial carcinoma (EC).

RESULTS

All of the 8 NPE showed moderate bax mRNA expression. In 1 of 6 SCH, 2 of 6 AH and 27 of the 42 EC (64.3%), there was overexpression of bax mRNA. In endometrial carcinoma, with the progression of clinical stage, increase in histologic grade and in depth of invasion to muscle layer, and lymph node metastasis, the positive rate of bax overexpression was correspondingly increased.

CONCLUSION

The results suggest that bax expression affects the balance between the endometrial cell proliferation and apoptosis. Bax might play an important role in carcinogenesis and tumor progression of endometrial carcinoma. As a high risk factor it can be used to evaluate the biological behavior of endometrial carcinoma.

Determination of sialic acids by liquid chromatography–mass spectrometry

Sialic acids are widely found in nature as components of oligosaccharide units in mucins, glycoproteins and other microbial polymers. Existing methods for determining these acids are long, tedious, and not specific. A simple, rapid, and sensitive method for determining the most commonly occurring acids, N-acetylneuraminic and N-glycolylneuraminic acid, using LC-MS is described. Standard solutions of the sialic acids with the internal standard, N-acetylneuraminic acid methyl ester, were quantitatively analyzed by positive ion electrospray ionization. Fetuin was used as a model glycoprotein and the hydrolysate was injected directly onto an ES Industries AquaSep 3 microm 150x4.6 mm column eluted with a 0.1% aqueous formic acid mobile phase at a flow-rate of 0.5 ml/min. Detection was achieved using the Finnigan Navigator MS system in the selected ion monitoring mode for the protonated molecular ions at m/z 310, 324, and 326. The linearity over the dynamic range 10 to 1000 ng of sialic acids on-column had a correlation coefficient greater than 0.999. The amount of sialic acids found in the fetuin hydrolysate was in agreement with values reported in the literature.

The design of new molecular "light switches" for DNA

Two novel ruthenium(II) complexes, [Ru(pztp)2(phen)](ClO4)2 and [Ru(pztp)2(bpy)] (ClO4)2, have been synthesized and characterized by UV/Vis and 1H NMR spectroscopies and mass spectrometry. The MeCN solutions of both complexes display fluorescence that was found to be highly sensitive to the presence and concentration of water. The complexes behave like a "light switch" for DNA in that they do not luminesce in water but were "turned on" in the presence of DNA and show emission enhancement with the increase of DNA concentration. Their DNA binding behavior was also studied by absorption spectroscopy and viscosity measurements, which suggest that the DNA-complex interaction involves intercalation of the metal-bound pztp ligand into the base pairs of duplex DNA.

DNA-binding and photocleavage studies of cobalt(III) polypyridyl complexes:

Two complexes of [Co(phen)2IP]3+ (IP=imidazo[4,5-f][l,10]phenanthroline) and [Co(phen)2PIP]3+ (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV/VIS, IR, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, cyclic voltammetry, viscosity measurements and DNA cleavage assay. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both of the complexes bind to CT DNA by intercalation via IP or PIP into the base pairs of DNA. [Co(phen)2PIP]3+ binds more avidly to CT DNA than [Co(phen)2IP]3+, which is consistent with the extended planar and pi system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.

Several log increase in therapeutic transgene delivery by distinct adeno-associated viral serotype vectors

We previously demonstrated that rAAV vectors carrying human and canine factor IX (FIX) cDNA can infect, stably persist, and secrete functional human and canine FIX following direct intramuscular injection. In an attempt to improve FIX protein secretion for eventual therapeutic use, we set out to determine if alteration of the AAV capsid would affect skeletal muscle transduction and factor IX secretion. Two reasons to pursue this question were (1) the persistence of high-titer neutralizing antibody (NAB) to AAV2 and (2) our previous study that supported a restricted tropism of muscle fiber types to AAV2 transduction. Using an identical CMV/canine factor IX (cFIX) expression cassette, we cross-packaged this genome into virions generated from each of the five AAV serotypes. In a dose-response assay, equivalent amounts of rAAV/cFIX serotypes were tested in vitro and in vivo. In tissue culture cells, FIX antigen levels secreted into the supernatant varied depending on the AAV serotype used; type 2 transduced maximally, with serotypes 3, 1, 5, and 4, respectively, expressing lower levels. However, when the same viruses were tested in vivo using immunodeficient NOD/SCID animals, we obtained surprisingly different results. While the time to onset of detectable serum levels appeared the same for all serotypes, types 1, 3, and 5 produced 100- to 1000-fold more cFIX than type 2. In fact, 12 weeks after transduction, type 1 continued to express levels of cFIX on average at 80 microg/ml followed by type 5 (6.52 microg/ml), type 3 (3.27 microg/ml), type 4 (258 ng/ml), and finally type 2 (90 ng/ml). Coagulant activity of cFIX as measured by aPTT supported the circulating levels measured by ELISA demonstrating the secreted protein was functional, and RT-PCR of injected tissue correlated with the serotype-specific transduction data. In summary, we found significant differences in cFIX expression upon introducing various rAAV serotypes into mouse muscle. These data have direct bearing on the design of AAV gene therapy clinical trials for hemophilia and should also extend to most therapeutic transgenes.

Malignant mixed mesodermal tumors of the ovary: preoperative diagnosis

Early diagnosis of malignant mixed mesodermal tumors of the ovary is very difficult because of the rarity and the insidious onset. The purpose of this report is to review the magnetic resonance imaging features of an ovarian malignant mixed mesodermal tumor, which occurred in a 52-year-old woman, aiding in the differential diagnosis.

[Methylation and expression of the p16 gene in endometrial carcinoma]

OBJECTIVE

To analyse the relationship between methylation status of the 5' CpG island and mRNA expression of the p16 gene in endometrial carcinoma.

METHODS

Methylation status of p16 gene was determined by methylation-sensitive restriction enzymes, PCR and p16 mRNA expression was evaluated by RT-PCR in a series of 8 specimens with normal endometrium(NE), 6 with simple and complex hyperplasia(SCH), 6 with atypical hyperplasia (AH) and 38 with endometrial carcinoma(EC).

RESULTS

Eight specimens of NE displayed no methylation and showed normal expression of the p16 mRNA. In 1 of the 6 AH and 13 of the 38(34.21%) EC, there was methylation of p16 exon 1; 5 of the 6 SCH showed overexpression of p16 mRNA, 4 of the 6 AH and 27 of the 38 (71.05%) EC exhibited decrease or loss of p16 mRNA expression.

CONCLUSION

Hypermethylation of p16 gene is an early event of endometrial carcinogenesis and is associated with the progression of endometrial carcinoma. Hypermethylation is highly correlated with inhibition of p16 gene transcription.

[Growth inhibition effect of 5-aza-CdR on endometrial carcinoma xenografted in nude mice by p16 gene demethylation]

OBJECTIVE

To study the antitumor effect and mechanism of 5-aza-CdR on endometrial carcinoma xenografted in nude mice.

METHODS

The effects of 5-aza-CdR on tumor growth inhibition were observed on human endometrial carcinoma xenografted in nude mice. The methylation status of the 5' CpG island of the p16 gene was evaluated using methylation-sensitive restriction enzymes and polymerase chain reaction. p16 mRNA expression was determined by reverse transcription-polymerase chain reaction.

RESULTS

The inhibition rates of the tumor were 79.10% in 5-aza-CdR group (P < 0.01), 90.32% in 5-aza-CdR + DDP group (P < 0.01), and 10.13% in DDP group (P > 0.05), respectively, in comparison with control group. The methylation level of p16 gene was gradually decreased and the p16 mRNA expression restored after exposure to 5-aza-CdR.

CONCLUSION

Our data show that 5-aza-CdR may inhibit tumor growth by reactivating growth-regulatory gene silenced by de novo methylation.

Sustained expression of human factor VIII in mice using a parvovirus-based vector

Persistent therapeutic levels of human factor VIII (hFVIII) would signify a major advance in the treatment of hemophilia A. Here we report sustained expression of hFVIII in immunocompetent mice using recombinant adeno-associated virus (rAAV) vectors. AAV can stably transduce liver cells, the target tissue for efficient hFVIII production. Because of rAAV packaging constraints, we tested 2 constructs using small regulatory elements designed for liver-specific transgene expression linked to B-domain-deleted hFVIII (BDD-hFVIII) cDNA. More than 10(12)/mL rAAV/BDD-hFVIII virion particles were generated using a transfection scheme that eliminates adenovirus. Coatest and APTT assays confirmed the production of functional BDD-hFVIII protein after transduction of 293 and HepG2 cells. In vivo experiments were performed in C57BL/6 and NOD/scid mice receiving 10(10-11) rAAV/hFVIII particles via portal vein injection. All C57BL/6 mice tested developed anti-hFVIII antibody. In contrast, NOD/scid mice expressed hFVIII reaching 27% of normal human plasma levels. As expected, we could not detect hFVIII antigen from plasma samples isolated from control animals receiving equivalent doses of rAAV expressing enhanced green fluorescent protein (EGFP). Transgene mRNA expression was detected primarily in the liver and histologic analysis of the liver revealed no pathologic abnormalities. These results demonstrate a promising approach for treatment of hemophilia A. (Blood. 2000;95:1594-1599)

Sterol carrier protein-2 suppresses microsomal acyl-CoA hydrolysis

Although sterol carrier protein 2 (SCP-2) has long been regarded primarily as a sterol transfer protein, its actual physiological function is not known. The recent discovery that SCP-2 binds long chain fatty acyl-CoAs (LCFA-CoAs) with high affinity suggests additional roles for SCP-2 in cellular utilization of LCFA-CoAs for synthesis of glycerides and cholesterol esters. Concomitant to these anabolic pathways, LCFA-CoAs are also degraded by cellular hydrolases. The purpose of the work presented herein was to determine if SCP-2 altered the aqueous pool of LCFA-CoA by (i) extracting LCFA-CoA from microsomal membranes, and (ii) protecting LCFA-CoA from microsomal hydrolase activity. The data demonstrated for the first time that SCP-2 increases the aqueous pool of oleoyl-CoA by increasing the aqueous/membrane distribution oleoyl-CoA by 2.4-fold. In addition, SCP-2 inhibited the hydrolysis of oleoyl-CoA by microsomal acyl-CoA hydrolase 1.6-2.4 fold, depending on the concentration of oleoyl-CoA. By simultaneously extracting LCFA-CoA from membranes and inhibiting LCFA-CoA degradation SCP-2 may potentiate LCFA-CoA transacylation and modulate the role of LCFA-CoAs as intracellular signaling molecules.

pRB-dependent, J domain-independent function of simian virus 40 large T antigen in override of p53 growth suppression

Simian virus 40 (SV40) large T antigen (LT) can immortalize and transform many cell types. These activities are attributed in large part to the binding and functional inactivation by LT of two major tumor suppressors: p53 and the retinoblastoma protein, pRB. Most effects of LT on pRB have been shown to additionally require an intact J domain, which mediates binding to Hsc70. We show here that the J domain is not required for p53 override in full-length LT. Although LT binds p53, it was shown previously that overcoming a p53-induced cell cycle arrest requires binding to pRB family members (R. S. Quartin et al., J. Virol. 68:1334-1341). We demonstrate that an LT mutant defective for pRB family member binding (K1) can be complemented for efficient override of p53 arrest by a construct encoding the first 135 amino acids of LT with a J domain-inactivating mutation, H42Q. Hence, complementation does not require the J domain, and pRB binding by LT is important for more than dissociating pRB-E2F complexes, which is J dependent. In accordance with this notion, LT alleviates pRB small-pocket-mediated transcriptional repression independently of the J domain. The LT K1 mutant can also be complemented for p53 override by small t antigen (st) in a manner independent of its J domain. Our observations underscore the importance of multiple SV40 functions, two in LT and one in st, that act cooperatively to counteract p53 growth suppression.

New ice-binding face for type I antifreeze protein

Type I antifreeze protein (AFP) from winter flounder is an alanine-rich, 37 amino acid, single alpha-helix that contains three 11 amino acid repeats (Thr-X(2)-Asx-X(7)), where X is generally Ala. The regularly spaced Thr, Asx and Leu residues lie on one face of the helix and have traditionally been thought to form hydrogen bonds and van der Waals interactions with the ice surface. Recently, substitution experiments have called into question the importance of Leu and Asn for ice-binding. Sequence alignments of five type I AFP isoforms show that Leu and Asn are not well conserved, whereas Ala residues adjacent to the Thr, at right angles to the Leu/Asn-rich face, are completely conserved. To investigate the role of these Ala residues, a series of Ala to Leu steric mutations was made at various points around the helix. All the substituted peptides were fully alpha-helical and remained as monomers in solution. Wild-type activity was retained in A19L and A20L. A17L, where the substitution lies adjacent to the Thr-rich face, had no detectable antifreeze activity. The nearby A21L substitution had 10% wild-type activity and demonstrated weak interactions with the ice surface. We propose a new ice-binding face for type I AFP that encompasses the conserved Ala-rich surface and adjacent Thr.

Evi-1 and MDS1-Evi-1 genes in pathogenesis of myelodysplastic syndromes and post-MDS acute myeloid leukemia

OBJECTIVE

To investigate expression of Evi-1 and MDS1-Evi-1 genes in myelodysplastic syndromes (MDS) and post-MDS acute myeloid leukemia (post-MDS AML), and its role in pathogenesis or progression of MDS and post-MDS AML.

METHODS

Expression of Evi-1 and MDS1-Evi-1 genes was examined in 31 MDS, 11 post-MDS AML, and 34 de novo AML patients by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Evi-1 expression was not detected in bone marrow samples of 8 normal controls, but low MDS1-Evi-1 expression levels (MDS1-Evi-1/GAPDH < 0.1) were detected in 3 of the 8 controls. Evi-1 RNA was expressed in 1 of 8 RA, 8 of 13 RAEB and 6 of 9 RAEB-T patients, and the percentage of Evi-1 expression in RAEB(T) patients was higher than that in RA (P < 0.05). MDS1-Evi-1 expression was detected in 5 of 8 RA, 9 of 13 RAEB and 5 of 9 RAEB-T patients, and MDS1-Evi-1 expression levels (MDS1-Evi-1/GAPDH > 0.1) were markedly higher than those in the controls. Evi-1 expression was gradually increased in 4 of 5 RAEB-T patients with transformation from MDS to AML. The percentages of Evi-1 and MDS1-Evi-1 expression in post-MDS AML patients were significantly (P < 0.01 and P < 0.05 respectively) higher than those in de novo AML. The colonies of hematopoietic progenitor cells were decreased in Evi-1 and MDS1-Evi-1-positive MDS patients as compared with those in Evi-1 and MDS1-Evi-1-negative patients.

CONCLUSION

Abnormal expression of the Evi-1 gene and overexpression of MDS1-Evi-1 gene may play a role in the pathogenesis or progression of MDS and post-MDS AML.

Persistent expression of canine factor IX in hemophilia B canines

We previously demonstrated that direct intramuscular injection of recombinant adeno-associated virus (rAAV) carrying the human FIX (hFIX) cDNA can safely be administered to hemophilic B canines and express human factor IX protein; however, the functional activity of the hFIX protein could not be assessed due to anti-human FIX antibody (inhibitor) formation. To test the therapeutic efficacy of rAAV in hemophilic dogs, rAAV type 2 (rAAV2) carrying canine FIX (cFIX) cDNA was injected into the skeletal muscle of two dogs at doses of 1012-13particles. Circulating cFIX protein levels were maintained for 1 year at levels of 1-2% of normal. Hemostatic correction (WBCT and APTT) paralleled plasma FIX antigen levels. Both dogs still required plasma infusion for spontaneous and traumatic bleeding events. Inhibitors to cFIX protein were not detected in either animal by Bethesda assay. Neutralizing antibodies directed against AAV-2 capsid were pronounced and persistent. Vector DNA and mRNA transcripts were detected only at the injected skeletal muscle tissue. Analysis of both high and low molecular weight DNA identified both replicative episomal and integrated AAV species. These results demonstrate that persistent secretion of the FIX transgene protein, necessary for successful gene therapy of hemophilia B, can be achieved using the parvovirus-based rAAV vector

Microsomal long chain fatty acyl-CoA transacylation: differential effect of sterol carrier protein-2

The recent discovery that sterol carrier protein-2 (SCP-2) binds long chain++ (LCFA-CoA) with high affinity (A. Frolov et al., J. Biol. Chem. 271 (1997) 31878-31884) suggests new possible functions of this protein in LCFA-CoA metabolism. The purpose of the present investigation was to determine whether SCP-2 differentially modulated microsomal LCFA-CoA transacylation to cholesteryl esters, triacylglycerols, and phospholipids in vitro. Microsomal acyl-CoA:cholesterol acyltransferase (ACAT) activity measured with liposomal membrane cholesterol donors depended on substrate LCFA-CoA level, mol% cholesterol in the liposomal membrane, and total amount of liposomal cholesterol. As compared to basal activity without liposomes, microsomal ACAT was inhibited 30-50% in the presence of cholesterol poor (1.4 mol%) liposomes. In contrast, cholesterol rich (>25 mol%) liposomes stimulated ACAT up to 6.4-fold compared to basal activity without liposomes and nearly 10-fold as compared to cholesterol pool (1.4 mol%) liposomes. Increasing oleoyl-CoA reversed the inhibition of microsomal ACAT by cholesterol poor (1.4 mol%) liposomes, but did not further stimulate ACAT in the presence of cholesterol rich (35 mol%) liposomes. In contrast, high (100 microM) oleoyl-CoA inhibited ACAT nearly 3-fold. This inhibition was reversed by LCFA-CoA binding proteins, bovine serum albumin (BSA) and SCP-2. SCP-2 was 10-fold more effective (mole for mole) than BSA in reversing LCFA-CoA inhibited microsomal ACAT. Concomitantly, under conditions in which SCP-2 stimulated ACAT it equally enhanced transacylation of oleoyl-CoA into phospholipids, and 5.2-fold enhanced oleoyl-CoA transacylation to triacylglycerols. In summary, SCP-2 appeared to exert its greatest effects on microsomal transacylation in vitro by reversing LCFA-CoA inhibition of ACAT and by differentially targeting LCFA-CoA to triacylglycerols. These data suggest that the high affinity interaction of SCP-2s with LCFA-CoA may be physiologically important in microsomal transacylation reactions.

[Metastatic tumors of the vulva: a report of 78 cases]

OBJECTIVE

To study the clinical characteristics, diagnosis and reasonable therapy for metastatic tumors of vulva.

METHODS

Seventy eight cases with metastatic tumors of the vulva were retrospectively reviewed. The cervical carcinoma was the most frequent primary site (61 cases), followed by the urethra (5 cases), vagina (4 cases), endometrium (3 cases), breast (2 cases), ovary (1 cases), rectum carcinoma (1 cases) and malignant lymphoma (1 cases).

RESULTS

The median age of this series was 55. 75.6%(59/78) of the patients subsequently developed vulvar metastasis from 15 days to 18 years after the primary tumors diagnosed, the median interval was 2.5 years. 61.5%(48/78) patients combined with primary site recurrence or other place metastasis, primary site recurrence were 35.4%, inguinal lymph node metastasis 45.8%, supraclavicular lymph node metastasis 8.3%, pelvic metastasis 8.3% and hematogenous metastasis 12.5% (liver, lung, skeleton). Radiotherapy was the main therapeutic approch, some cases combined with surgery and/or chemotherapy. The overall 1 year, 3 years and 5 years survival rates after vulvar metastatic occurrence were 65.4%, 29.5% and 16.7% respectively.

CONCLUSIONS

The prognosis of the vulva metastatic tumors was poor. Radiotherapy combine with surgery and/or chemotherapy can improve the survival.

Alternative roles for putative ice-binding residues in type I antifreeze protein

Two sets of variants of type I antifreeze protein have been synthesized to investigate the role of Leu and Asn in the activity of this 37-residue alpha-helix. Leu and Asn flank the central two of four regularly spaced ice-binding Thr in the i-1 and i + 3 positions, respectively. All three residues project from the same side of the helix to form the protein's putative ice-adsorption site and are considered in some models to act together as an "ice-binding motif". Replacement of Asn by residues with shorter side chains resulted in either a small loss (Ala) or gain (Thr) of antifreeze activity. However, substitution of Asn by its slightly larger homologue (Gln) abolished thermal hysteresis activity. The Gln-containing peptide was very soluble, largely monomeric, and fully helical. Of the three variants in which Leu was replaced by Ala, two of the three were more active than their Leu-containing counterparts, but all three variants began to precipitate as the peptide concentration increased. None of the seven variants tested showed dramatic differences in ice crystal morphology from that established by the wild type. These results are consistent with a primary role for Leu in preventing peptide aggregation at the antifreeze protein concentrations (10 mg/mL) normally present in fish serum. Similarly the role for Asn may have more to do with enhancing the solubility of these rather hydrophobic peptides than of making a stereospecific hydrogen-bonding match to the ice lattice as traditionally thought. Nevertheless, the dramatic loss of activity in the Asn-to-Gln replacement demonstrates the steric restriction on residues in or near the ice-binding site of the peptide.

Use of a heterodimeric coiled-coil system for biosensor application and affinity purification

The two-stranded alpha-helical coiled-coil is now recognized as one of nature's favorite ways of creating a dimerization motif. Based on the knowledge of protein folding studies and de novo design model systems, a novel heterodimeric coiled-coil protein was synthesized. The heterodimeric E/K coiled-coil was constructed with two distinct peptides (E and K) that will spontaneously associate into a full helical coiled-coil structure in solution. Equilibrium CD, NMR and real time biosensor kinetics experiments showed that the E/K coiled-coil is both structurally (deltaG(unfold)=11.3 kcal/mol) and kinetically (Kd approximately 1 nM) stable in solution at neutral pH. The engineered coiled-coil had been applied as a dimerization and capture domain for biosensor based applications and used in an expression/detection/affinity chromatography system. Specific test examples demonstrated the usefulness of the E/K heterodimeric system in these applications. The universality of coiled-coil as a dimerization motif in nature and our ability to design and synthesize these proteins suggest a wide variety of applications.

Binding of an oligopeptide to a specific plane of ice

The alpha-helical antifreeze protein (AFP) from winter flounder inhibits ice growth by binding to a specific set of pyramidal surface planes that are not otherwise macroscopically expressed. The 37-residue AFP contains three 11-amino acid repeats that make a stereo-specific fit to the ice lattice along the <01-12> direction of the (20-21) and equivalent binding planes. When the AFP was shortened to delete two of the three 11-amino acid ice-binding repeats, the resulting 15-residue peptide and its variants were less helical and showed no antifreeze activity. However, when the helicity of the peptide was reinforced by an internal lactam bridge between Glu-7 and Lys-11, the minimized AFP was able to stably express the pyramidal plane (20-21) on the surface of growing ice crystals. This dynamic shaping of the ice surface by a single ice-binding repeat provides evidence that AFP adsorption to the ice lattice is not an "all-or-nothing" interaction. Instead, a partial interaction can help develop the binding site on ice to which the remainder of the AFP (or other AFP molecules) can orient and bind.

Effect of mobile phase on the oligomerization state of alpha-helical coiled-coil peptides during high-performance size-exclusion chromatography

Important structural motifs involving amphipathic helices include two-stranded and multiple-stranded coiled-coils. High-performance size-exclusion chromatography (HPSEC) is a useful tool to examine both the oligomerization state of coiled-coils as well as the stability of such motifs, due to the facile manipulation of the mobile phase and the lack of interaction of the peptide solutes with the stationary phase. In the present study, HPSEC was applied to two series of de novo designed model amphipathic alpha-helical peptides with the sequences (1) Ac-(E-A-L-K-A-E-I)n-E-A-C-K-A-amide, where n = 1 or 3, Ac-E-I-(E-A-L-K-A-E-I)4-E-A-C-K-A-amide and (2) Ac-(K-L-E-A-L-E-A)n-amide, where n = 1, 2 or 4. Observation of the retention behaviour of Series 1 under both denaturing and non-denaturing conditions at pH 7.0 offered insights into the effect of polypeptide chain length and disulphide bridge formation on the stability of alpha-helical coiled-coils. In contrast, the Series 2 peptides showed promise as peptide standards to monitor the effect of environment on the multi-strandedness of coiled-coils, since the 28-residue peptide of this series was eluted as a monomer, dimer or trimer depending on mobile phase conditions.

A diminished role for hydrogen bonds in antifreeze protein binding to ice

The most abundant isoform (HPLC-6) of type I antifreeze protein (AFP1) in winter flounder is a 37-amino-acid-long, alanine-rich, alpha-helical peptide, containing four Thr spaced 11 amino acids apart. It is generally assumed that HPLC-6 binds ice through a hydrogen-bonding match between the Thr and neighboring Asx residues to oxygens atoms on the {2021} plane of the ice lattice. The result is a lowering of the nonequilibrium freezing point below the melting point (thermal hysteresis). HPLC-6, and two variants in which the central two Thr were replaced with either Ser or Val, were synthesized. The Ser variant was virtually inactive, while only a minor loss of activity was observed in the Val variant. CD, ultracentrifugation, and NMR studies indicated no significant structural changes or aggregation of the variants compared to HPLC-6. These results call into question the role of hydrogen bonds and suggest a much more significant role for entropic effects and van der Waals interactions in binding AFP to ice.