title: Silica condensation by a silicatein α homologue involves surface-induced transition to a stable structural intermediate forming a saturated monolayer.
abstract: Silicatein α exists within the protein filament of silica spicules of the marine sponge Tethya aurantium in a predominantly β-sheet structure. However, it is produced in a soluble form with mixed α-helix/β-sheet structure akin to its cathepsin L homologue. To understand this conformational transition in the context of enzyme catalyzed silica condensation, we used a functional, recombinant silicatein α termed 4SER. In solution, 4SER becomes conformationally unstable at pH 7 and readily unfolds to a soluble β-sheet intermediate, losing the majority of its helical structure. This β-sheet intermediate is present following adsorption of 4SER to a silica surface from solution. 4SER is particularly surface active, forming a near saturated monolayer on SiO2 from low bulk concentrations, without transition to multilayers at high bulk concentrations. The adsorbed intermediate remains stable during silica condensation and drying. We propose that the β-sheet structure for silicatein α in marine sponge spicules represents a stable structural intermediate, formed upon adsorption to the silica surface.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS United Kingdom, Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose St, Glasgow, G1 1XJ United Kingdom, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX United Kingdom, College of Medical, Veterinary and Life Sciences, Institute of Molecular, Cell & Systems Biology, University of Glasgow, Glasgow, G12 8QQ United Kingdom, and Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow, G4 0RE United Kingdom.
authors.forename: Siddharth V
authors.initials: SV
authors.lastname: Patwardhan
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Holt
authors.forename: Sharon M
authors.initials: SM
authors.lastname: Kelly
authors.forename: Michaela
authors.initials: M
authors.lastname: Kreiner
authors.forename: Carole C
authors.initials: CC
authors.lastname: Perry
authors.forename: Christopher F
authors.initials: CF
authors.lastname: van der Walle
mesh_terms: D000327:Adsorption; D000818:Animals; D002403:Cathepsins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D011161:Porifera / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties
chemical_list: C112571:silicatein alpha; D012822:Silicon Dioxide; D002403:Cathepsins