title: Structural properties of recombinant nonrepetitive and repetitive parts of major ampullate spidroin 1 from Euprosthenops australis: implications for fiber formation.
abstract: Spider dragline silk proteins, spidroins, have a tripartite composition; a nonrepetitive N-terminal domain, a central repetitive region built up from many iterated poly-Ala and Gly rich blocks, and a C-terminal nonrepetitive domain. It is generally believed that the repetitive region forms intermolecular contacts in the silk fibers, while precise functions of the terminal domains have not been established. Herein, thermal, pH, and salt effects on the structure and aggregation and/or polymerization of recombinant N- and C-terminal domains, a repetitive segment containing four poly-Ala and Gly rich coblocks, and combinations thereof were studied. The N- and C-terminal domains have mainly alpha-helical structure, and interestingly, both form homodimers. Dimerization of the end domains allows spidroin multimerization independent of the repetitive part. Reduction of an intersubunit disulfide in the C-terminal domain lowers the thermal stability but does not affect dimerization. The repetitive region shows helical secondary structure but appears to lack stable folded structure. A protein composed of this repetitive region linked to the C-terminal domain has a mainly alpha-helical folded structure but shows an abrupt transition to beta-sheet structures upon heating. At room temperature, this protein self-assembles into macroscopic fibers within minutes. The secondary structures of none of the domains are altered by pH or salt. However, high concentrations of phosphate affect the tertiary structure and accelerate the aggregation propensity of the repetitive region. Implications of these results for dragline spidroin behavior in solution and silk fiber formation are discussed.
authors.affiliation: Department of Anatomy, Physiology and Biochemistry, Biomedical Centre, Swedish University of Agricultural Sciences, SE-751 23 Uppsala, Sweden. my.hedhammar@afb.slu.se
authors.forename: My
authors.initials: M
authors.lastname: Hedhammar
authors.forename: Anna
authors.initials: A
authors.lastname: Rising
authors.forename: Stefan
authors.initials: S
authors.lastname: Grip
authors.forename: Alejandra Saenz
authors.initials: AS
authors.lastname: Martinez
authors.forename: Kerstin
authors.initials: K
authors.lastname: Nordling
authors.forename: Cristina
authors.initials: C
authors.lastname: Casals
authors.forename: Margareta
authors.initials: M
authors.lastname: Stark
authors.forename: Jan
authors.initials: J
authors.lastname: Johansson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005349:Fibroins / Q000096:biosynthesis / Q000737:chemistry*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry*; D020449:Repetitive Sequences, Amino Acid; D013112:Spiders / Q000737:chemistry*; D013696:Temperature
chemical_list: D011993:Recombinant Fusion Proteins; C086087:spidroin 1; D005349:Fibroins