Patent Abstract:
the present invention is directed to a method of producing spider dragline and / or flagelliform proteins . the invention is further directed to a method of producing spider threads and to a dragline / flagelliform protein or dragline / flagelliform protein thread produced by these methods . the invention further provides the use of these proteins / threads in the field of biotechnology and / or medicine , in particular in the manufacture of wound closure or coverage systems , suture materials and in the manufacture of replacement materials , preferably artificial cartilage or tendon materials .

Detailed Description:
the improvement provided herein was based on the idea to express and study the two major protein constituents of araneus diadematus dragline silk simultaneously . since insects belong to the same phylum as spiders , the inventors chose the insect cell line sf9 ( derived from the fall armyworm spodoptera frugiperda ), for the expression of adf - 3 and adf - 4 using baculoviruses as vectors . recombinant baculoviruses were generated containing partial cdnas of adf - 3 and adf - 4 ( 14 ). in order to monitor synthesis , both proteins were provided with a his 6 - tag . to exclude artificial influences caused by the tag , versions without his 6 - tag were also employed . the recombinant viruses were used to infect sf9 cells for production of the spider silk proteins in the cytoplasm . after 3 days of incubation , infected cells were lyzed by sonification and insoluble cell contents were separated from soluble material by sedimentation . the sediment was dissolved in guanidinium thiocyanate ( gdmscn ) prior to analysis by immunoblotting . while a large fraction of adf - 3 was found to be soluble , adf - 4 was almost entirely insoluble three days after infection under the conditions employed ( fig1 a ) and independent from the presence of the his 6 - tag ( fig4 a ). surprisingly , investigating the aggregates in adf - 4 expressing cells revealed filaments that coiled throughout the cytoplasm , whereby most of the cells contained only one or few filaments of a uniform width ( fig1 b ). in contrast , cells infected with control viruses or the adf - 3 encoding virus never produced such filaments ( fig4 c , d ). immunofluorescence performed on the infected cells using anti - his 6 antibodies showed specific staining of the filaments thus confirming that the filaments were composed of adf - 4 ( fig1 b ). next , the inventors investigated whether adf - 3 and adf - 4 can co - assemble into filaments . the inventors generated a recombinant baculovirus containing both adf - 3 and adf - 4 under different and independent promoters , using the pfastbacdual donor plasmid . infection of sf9 cells with this virus resulted in synthesis of both proteins and the formation of protein filaments that showed similar appearance in comparison to the filaments formed by synthesis of adf - 4 alone ( fig4 b ). interestingly , filaments assembled in the dual expression system were entirely formed by adf - 4 with no incorporated or stably associated adf - 3 ( fig1 c and data not shown ). in order to study whether the apparent self - assembly is solely based on properties of adf - 4 or whether additional factors or modifications are involved , the inventors created a recombinant baculovirus coding for a secreted form of his 6 - adf - 4 . infection of cells with this virus led to accumulation of adf - 4 in the culture media of the cells ( fig1 d ). immunofluorescence revealed the abundance of adf - 4 containing secretory vesicles at the cell surface of the infected cells ( fig1 e ). strikingly , the inventors did not observe any formation of adf - 4 filaments neither in compartments of the host cells nor in the culture media . silk thread formation generally depends on the protein concentration as well as on additional factors . interestingly the intracellular ph 6 . 3 of sf9 cells corresponds to the ph in the spinning dope prior to silk thread assembly ( 19 ). further factors required for adf - 4 filament assembly in the cytosolic environment remain elusive . investigating the self - assembling properties of adf - 4 in vitro stressed the importance of additional factors . soluble adf - 4 was readily obtained by dissolving filaments in 6 m gdmscn . dissolved adf - 4 rapidly aggregated upon removal of gdmscn by dialysis or dilution . however , the adf - 4 aggregates formed in vitro showed neither fibrillar structures nor did they display the chemical stability of adf - 4 filaments formed inside the sf9 cells ( see below and fig4 e , f ). the above findings indicate the importance of the specific cytosolic environment , which may include additional , so far unresolved , cytoplasmatic factors important for controlled self - assembly . next the inventors characterized the morphology of adf - 4 filaments . the diameters of filaments ranged from 200 nm to 1 μm , however for each single filament the diameter was found to be constant . furthermore , the filaments showed lengths up to 100 μm and often terminated in knots , branches or formed closed circles ( fig2 a , d , e ). filaments displayed a smooth surface and were often associated with nanofibers ( diameter ˜ 5 nm ) and other protein aggregates ( fig2 ). immunoblotting , and immunoelectron microscopy indicated that filaments and associated assembly forms were composed of adf - 4 ( fig2 c , 3 a ). besides adf - 4 no other abundant protein could be detected in filaments as visualized by sds - page analysis followed by silver staining ( fig3 a ). the low number of filaments per cell and the recruitment of almost the entire cellular adf - 4 into the aggregates indicated that self - assembly of adf - 4 in sf9 cells is likely to be a nucleated process , which previously has been also suggested for the silk spinning process of bombyx mori ( 20 ). the size of the filaments formed in the sf9 cells seemed to be constrained by the volume of the cells making them too short for mechanical force measurements typically performed with silk threads ( 21 ). however , the inventors were able to analyze the chemical stability of wet and dry adf - 4 filaments in comparison to natural dragline silk threads of a . diadematus . dragline threads have been reported to be insoluble in many denaturing agents ( 22 ). application of 2 % sodium dodecylsulfate ( sds ) and 8 m urea apparently had no effect on the structure of adf - 4 filaments and dragline threads after 30 s of exposure ( fig3 and data not shown ). immersion of the filaments in 6 m guanidinium chloride ( gdmcl ) did not lead to solubilization of either adf - 4 filaments or dragline threads , although it did lead to swelling of dragline silk . such swelling is likely caused by fibre supercontraction ( 21 ) which has previously been described for spider silks immersed in aqueous solutions and which results from reformation of hydrogen bonds in the amorphous matrix ( 21 ). in contrast to the denaturants mentioned above , a small drop of 6 m gdmscn completely dissolved adf - 4 filaments as well as dragline threads within seconds ( fig3 ). in consequence the inventors conclude that both structures share molecular interactions , which are responsible for chemical resistance to specific denaturants . the partial cdnas of adf - 3 and adf - 4 ( gi | 1263286 ; gi | 1263288 in pbluescriptsk +) were kindly provided by john gosline ( vancouver , canada ). the cdnas were cloned into pfastbac ™ donor plasmids from invitrogen . sequences coding for peptide tags were provided 5 ′- terminal to the gene fragments . for his 6 - tagged proteins , genes were excised from the host vector using spei / xhoi and ligated with equally digested pfastbac ™ hta . for t7 - taged ( 23 ) proteins , genes were first cloned into pet21 from novagen using xhoi and ecori . the insert including the t7 - tag coding region was then excised with bglii and xhoi and ligated with pfastbac ™ 1 digested with bamhi / xhoi . for co - expressing adf - 3 and adf - 4 , both genes were cloned into pfasbac ™ dual and provided with sequences coding for t7 - and s - tags ( 24 ). the adf - 4 gene was excised from pet21 - adf - 4 with bglii / xhoi and ligated with pfasbac ™ dual cleaved with nhei / bamhi . two synthetic oligonucleotides ( mwg biotech ) were annealed to provide an s - tag coding sequence , which resulted in double stranded dna with nhei / bamhi - compatible single strand extensions : pet21 - adf - 3 was digested with nhei / bamhi to remove the t7 - tag coding region . the vector was then ligated with the s - tag encoding dna . the s - tagged adf - 3 was cloned into pfasbac ™ dual - adf - 4 using xhoi / xmai . in the dual construct , adf - 3 and adf - 4 were under the control of the independent p10 ( 25 ) and polyhedrin ( 26 ) promoters . the sequence coding for the secretion signal of honeybee melittin was amplified by pcr using the pmib / v5 - hisa vector ( invitrogen ) as template and the following primers containing cpoi restriction sites : 5 ′- ccttcc cggtccg ccatgaaattcttagtcaac ( seq id no : 7 ) 5 ′- ccttcc cggaccg ggcatagatgtaagaaat ( seq id no : 8 ) the resulting pcr product was cut with cpoi and ligated into pfastbac ™ hta - adf - 4 digested likewise . positive clones were checked for orientation and correctness by sequencing . sf9 ( spodoptera frugiperda ; atcc #: crl - 1711 ) cells were propagated at 27 ° c . in bioinsect - 1 serum - free insect cell culture medium ( biological industries ). sf9 cells were grown either as monolayers on cover slips in 6 well plates or in shaker flasks agitated at 80 rpm . competent e . coli dh10bac cells , containing bacmid ( baculovirus shuttle vector plasmid ) and a helper plasmid , were used to generate recombinant bacmids according to the manufacturer &# 39 ; s protocol ( invitrogen ). insertion of the gene into the bacmid was verified by pcr . sf9 cells were transfected with recombinant bacmid dna using escort transfection reagent ( sigma - aldrich ) in 6 - well plates . the cells were incubated for 5 h at 27 ° c ., rinsed , and incubated for another 72 h . media were harvested , centrifuged , and the virus - containing supernatant was tittered by plaque assays . sf9 cells ( 3 × 10 6 cells / ml ) were infected with the recombinant viruses at various mois ( multiplicity of infection ) ranging from 0 . 1 to 10 . three days post infection ( pi ), cells were harvested by centrifugation at 500 × g for 5 min . cells were resuspended at 1 . 2 × 10 7 cells / ml in 100 mm nacl , 20 mm n -( 2 - hydroxyethyl ) piperazine - n ′-( 2 - ethanesulfonic acid ) ( hepes ), ph 7 . 5 and lyzed by sonification . soluble and insoluble components were separated by centrifugation at 125 , 000 × g for 30 min . for further analysis , pellets were resuspended in 6 m gdmscn and dialyzed against 8 m urea . supernatant and pellet derived from 1 . 5 × 10 5 cells were loaded on 10 % tris - glycine polyacrylamide gels under reducing conditions and blotted onto pvdf membranes ( millipore ). spider silk proteins were detected using a mouse anti - his 6 monoclonal antibody ( sigma - aldrich , 1 : 10 , 000 ) or a mouse anti - t7 monoclonal antibody ( novagen , 1 : 10 , 000 ) and anti - mouse igg peroxidase conjugate ( sigma - aldrich , 1 : 5 , 000 ) as secondary antibody . an s - protein peroxidase conjugate ( novagen , 1 : 5 , 000 ) was used to directly detect s - tagged adf - 3 . cells grown on cover slips at 50 % confluency were infected with adf - 3 or adf - 4 containing recombinant viruses at moi = 10 . three days pi cells were fixed with methanol at − 20 ° c . cover slips were incubated with mouse anti - his 6 monoclonal antibody ( roche ) at a 1 : 300 dilution followed by texas red conjugated anti - mouse secondary igg at 1 : 500 dilution . cells were observed with an olympus bx51 fluorescence microscope and images were taken with a magnafire sp camera or analyzed by confocal microscopy . cells were resuspended at 1 . 2 × 10 7 cells / ml in 100 mm nacl , 20 mm hepes , ph 7 . 5 and lyzed by adding 2 % w / v sodium dodecylsulfate followed by incubation at 95 ° c . for 5 min . threads were sedimented at 5 , 000 × g followed by washing with 8 m urea and water bidest . purified filaments were resuspended in water bidest and incubated for 3 min on freshly cleaved mica ( afm ) or loaded on thermanox ® plastic cover slips ( nalgene nunc ) ( sem ). for afm , samples were rinsed with water bidest four times and air - dried prior to contact mode imaging using a multimode spm ( veeco ). for sem , samples were air dried after removal of the solution , vacuum coated with a gold layer and analyzed with a jsm - 5900lv ( jeol ltd .) at 20 kv . for tem ( jeol ltd .) analysis , filaments were adsorbed onto formvar coated grids and negatively stained with uranyl acetate . for immunostaining , fibers were incubated with mouse anti - his 6 antibodies followed by labeling with 18 nm gold - conjugated goat anti mouse igg . to rule out possible influences of the his 6 - tag on filament formation , t7 - tagged adf - 4 was synthesized in sf9 cells . the filament formation of t7 - tagged adf - 4 was apparently indistinguishable to that of his 6 - tagged adf - 4 ( fig4 a ). in sf9 cells co - expressing adf - 3 and adf - 4 , filaments could be detected that displayed an apparently indistinguishable morphology in comparison to filaments formed in cells producing only adf - 4 ( fig4 b ). although immunocytochemistry revealed fluorescent foci in adf - 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